The 19-year-old squandered a golden opportunity on the stroke of the break when he glanced a header wide, but made amends three minutes after the restart with a sweeping finish from Samir Nasri's pass.
Marko Arnautovic, reportedly a transfer target of an unnamed Chinese club, appeared to wave goodbye to the home fans as he was substituted in the second half, but this performance should give West Ham confidence about life after the Austrian.
Relive how the action unfolded in the capital derby courtesy of Sports Mole's minute-by-minute updates.
11.30amAfter both negotiating potential banana skins in the FA Cup, West Ham United and Arsenal return to Premier League action this lunchtime with an all-captail affair at the London Stadium. Both endured mixed fortunes over the festive period so three points today would be the perfect start to the next stage of the season...
11.36amMesut Ozil was expected to be available for the Gunners today after injury but the German is again conspicuous by his absence from the Arsenal squad. It is an unchanged side from the team which beat Fulham 4-1 in their last Premier League game with Unai Emery keeping faith in his three-man defence.
11.38amMost of this Arsenal team should be refreshed after an 11-day break, with only Sokratis Papastathopoulos, Sead Kolasinac, Alex Iwobi and Ainsley Maitland-Niles of the starters to also begin the FA Cup win over Blackpool. Teenager Maitland-Niles is enjoying his best run in the team - four straight league starts.
11.40amWest Ham's defence will have a difficult task today with the Premier League's top goalscorer Pierre-Emerick Aubameyang partnered by Alexandre Lacazette, both scorers in the win over Fulham which was the first time that the two strikers had scored in the same game since November's North London derby.
11.42amHector Bellerin is back on the bench and Shkodran Mustafi and Nacho Monreal are also fit to ease Unai Emery's defensive injury concerns. Lucas Torreira has proved to be an excellent signing but again has to settle for a place on the bench with Granit Xhaka and Matteo Guendouzi preferred in midfield.
11.44amThe big news from the West Ham camp is that Marko Arnautovic starts despite the uncertainty over his future. The Austrian is reportedly the subject of a big bid from China but the Londoners want to keep him, and that is no surprise following a goal return of eight in 17 this season, including three in his last two.
11.46amFormer Arsenal midfielder Samir Nasri keeps his place in the West Ham team after making his debut in the FA Cup win over Blackpool. The new signing, who has reunited with his old manager at Manchester City Manuel Pellegrini, made 125 appearances for the Gunners before forcing a move to the Etihad.
11.48amFelipe Anderson and Michail Antonio are also included in a West Ham starting lineup which appears designed to attack the visitors. Anderson has been West Ham's star performer this season with eight goals and two assists, while Antonio rediscovered his scoring touch with a couple of goals in December.
11.50amThat four-pronged offensive unit means that Declan Rice has extra responsibility as the holding midfielder today. While they seemingly face a battle to keep hold of Arnautovic, West Ham have tied down the future of another of their star assets, who recently signed a new long-term contract with the club.
11.52amPellegrini has made five changes to the lineup which started against Birmingham in the FA Cup last weekend. Lukasz Fabianski, Pablo Zabaleta, Aaron Cresswell, Mark Noble and Anderson all return, while Pedro Obiang, Andy Carroll and Robert Snodgrass drop out from their previous league game - a 2-2 draw with Brighton & Hove Albion.
11.54amWith Arnautovic's status at the club hanging in the balance and Javier Hernandez suffering from a new injury layoff, Carroll's first goal since April 2018 should give him a confidence boost and make him a useful weapon to Pellegrini off the bench. The target man has a good record against Arsenal too.
11.56amJudging by quotes from Arnautovic's brother, this could be one of his last games for the Hammers...
"West Ham bought Marko for peanuts," Danijel Arnautovic told talkSPORT this week. "They paid £20million for him, which is nothing in the current market. Now West Ham have a fantastic offer. It is close to double what they paid for him. "He wants to go to a new market and challenge for titles. This is what he wants. It is his great desire that West Ham accept the offer from China."
11.58amThe Arnautovic situation may seem familiar to Hammers fans, after Dimitri Payet forced his way out of the club in the January window of 2017. West Ham's owners caved on that occasion, but unlike the Frenchman, Arnautovic has not gone on strike and still looks as though he will be committed on the pitch. Whether that works in his favour or not we will have to wait and see...
12.00pmAfter a slow start to life under Pellegrini, West Ham have emerged as a force to be reckoned with in the Premier League, winning five of their past eight matches to climb into the top half of the table. Victory today could take them level with seventh-placed Leicester City on goal difference.
12.02pmHowever, there is still a feeling that they have not fully settled into their London Stadium surroundings, and their home form has been a little disappointing again this term. The Irons have lost five matches at home, one more than they have on their travels, and have not won either of their last two as hosts.
12.04pmThe Hammers have failed to keep a clean sheet in any of their last eight home Premier League games - stretching back to September's 0-0 stalemate with Chelsea - and that is their longest such streak since a run of 12 in 2009. They have kept two clean sheets away from home during that time.
12.06pmUnited have won their last two capital derbies, beating Crystal Palace and Fulham last month, but have lost on three of their four meetings with London's big boys this campaign including the reverse fixture with Arsenal in August, when the Gunners came from behind to record a 3-1 triumph.
12.08pmHEAD TO HEAD: In fact, West Ham have won just one of their last 21 Premier League matches against Arsenal, losing 16 of those. That sole victory came in August 2015 when they shocked Arsene Wenger's side at the Emirates Stadium through Cheikhou Kouyate and Mauro Zarate goals.
12.10pmThe Gunners are unbeaten in 11 away matches at West Ham in all competitions since November 2006. The Hammers have lost 29 Premier League matches against Arsenal - more than against any other side - the most recent of those a landmark one for Emery - his first victory as a Premier League boss.
12.12pmArsenal are without a win in their last four away matches in the Premier League, and have conceded nine goals in their last three including five in a thumping by Liverpool. The Gunners have not kept a single away clean sheet this season, having both scored and conceded in every away league game this term.
12.14pmOnly Tottenham Hotspur with 28 goals have scored more away goals this season than Arsenal's 22. The Gunners are unmatched when it comes to second-half goals though, with their total of 32 more than anybody else in the division. They have scored at least one in their last 20 Premier League matches.
12.16pmKey to Arsenal's free-scoring nature has been the form of Pierre-Emerick Aubameyang, who has 24 goals in 34 Premier League appearances since his arrival from Borussia Dortmund nearly a year ago. In that period, only Liverpool's Mohamed Salah (25) has found the net more often in the English top flight.
12.18pmAuba has quickly established himself as a fan favourite at Arsenal, and he has helped his cause with a strike in each of his last four Premier League London derbies, with six goals and two assists in total. The Gunners have lost just one of their six London derbies this season - going down 3-2 at Chelsea.
12.22pmA lot has been made of Nasri facing his former club, but there is another ex-Gunner in the West Ham ranks in the shape of goalkeeper Lukasz Fabianski. The Pole didn't make the grade at the Emirates but has come on leaps and bounds in recent years, and is now one of the most consistent stoppers in the league. Arguably, he would be Arsenal's number one if he was still at the club now.
12.24pmIndeed, Aubameyang vs. Fabianski could be a key battle today - both leaders in their respective fields this season
SCOUT: Aubameyang, the joint-leading #PL scorer (14), faces Fabianski, the keeper with the most saves this season (80).
12.26pmBENCH WATCH: Arsenal's bench looks a little stronger with the return of Bellerin and Monreal, although it is a little short in attacking firepower, with Aaron Ramsey, reportedly off to Juventus in the summer, their only proven goalscorer in reserve. A third one-time Arsenal player - Lucas Perez - will be hoping to make an impact if he is called upon, and Carroll and Snodgrass are also options to Pellegrini.
12.28pmPREDICTION: One thing that Arsenal have guaranteed on the road this season is goals, and I don't expect today to be any different. The strength of both teams is in their attacking units, so I am predicting an exciting 2-2 draw, a better result for the hosts than the visitors, no doubt.
1 minKICKOFF: Referee Jonathan Moss blows his whistle, and the West Ham fans blow their bubbles as the action gets underway...
3 minAntonio goes on a mazy early dribble but a heavy touch allows Koscielny to get across on the cover, just as the winger was threatening to burst into the area. This already has the feeling of an open game.
5 minKolasinac is in acres of space on the left edge of the area but Iwobi cannot find him, the pass intercepted by Issa Diop. The loose ball falls to Aubameyang and again Diop is on hand to make the block.
7 minA surging 60-yard run from Antonio right along the right touchline takes two or three Arsenal players out of the game. He cuts the ball inside to Noble, who exchanges a one-two with Arnautovic but cannot trouble Leno with a weak left-footed shot from 18 yards out.
9 minSHOT! Xhaka knocks a simple straight pass forward onto the chest of Lacazette, who is afforded the space to allow the ball to drop and cut across a right-footed volley which flies wide from 25 yards out.
11 minSHOT! Anderson recycles the ball from a deep West Ham corner, drifts inside Iwobi and Guendouzi with ease and tries to curl a left-footed shot into the top corner, but he is just as much awry as Lacazette was moments ago.
13 minSAVE! Again there is space in the middle of the West Ham defence and Lacazette surges into it, drawing the first significant save out of Fabianski with a powerful low effort which is blocked at the near post.
13 minAgain there is space in the middle of the West Ham defence and Lacazette surges into it, drawing the first significant save out of Fabianski with a powerful low effort which is blocked at the near post.
15 minGuendouzi overhits a simple pass which would have set up Aubameyang for a shooting opportunity. Arsenal's best chance is gone by the time the striker chases after the ball and stands up a cross which Lacazette heads harmlessly over the bar.
17 minThings continue to go from end to end in the early stages here, with West Ham attacking through Cresswell who skips past Maitland-Niles effortlessly and fizzes in a cross which was destined for Antonio at the back post before Leno dives out to intercept.
19 minNasri has seen plenty of the ball in the opening 20 minutes, and each of his touches are being greeted with boos from the visiting fans. The Frenchman seemingly has the freedom to roam and link up with Anderson on the left or Antonio on the right, something which Emery needs to be wary of.
21 minCrucial interception from Rice to prevent Lacazette from running onto a cross from Kolasinac, who had been released into the box by a clever flick from Iwobi. The wing-back has been a great offensive outlet for Arsenal recently and again their main threat today is coming from his left flank.
23 minGood play from Nasri earns West Ham a corner, from which Arsenal are yet to concede this season and Mustafi gets up high to make a towering clearance to ensure that record is sustained for now.
25 minCHANCE! How Nasri would love to score today, and he gets his first sight on goal here but drags a shot wide of the near post from an acute angle after collecting a return pass from Arnautovic, having started the move himself.
27 minAn early cross from Anderson is aimed at the aerial weapon that is Antonio at the back post. Koscielny refuses to take any chances by knocking the ball out for a corner which West Ham take short, and it comes to nothing.
29 minIt has been mostly the hosts on the front foot in the last 10 minutes. When Arsenal do get the ball forward, it has mostly been into Iwobi's feet and he has looked quite bright, but not always picked the right pass.
31 minCLOSE! Arnautovic and Nasri combine to hold the ball up and then tee up Anderson, who runs onto the layoff perfectly and lets off a right-footed drive from 20 yards which would have left Leno with no chance had it been a couple of yards to the right.
33 minArsenal are in a game here. They are not having it all their own way...
35 minSHOT! Guendouzi goes close for the Gunners, so close that the Arsenal fans at the far end of the ground briefly celebrate as if his 25-yard rocket had gone in, and not rustled the side-netting of Fabianski's goal.
37 minThe young midfielder is in the thick of the action again, requiring treatment from the Arsenal physio after an awkward fall during a tussle with Nasri. At worst it looks like a jarred shoulder so I'm sure Guendouzi will look to shake that off.
39 minIt seems as though Guendouzi will be fine to continue but Emery has not been shy of making half-time changes this season, so Torreira and Ramsey might be going through a vigorous warm up at the break.
41 minWest Ham waste a decent opening after working the ball nicely out to Antonio on the right, the former Nottingham Forest winger choosing to cut inside and shoot, sending his left-footed effort high and wide.
43 minGood energy levels on display from West Ham as they twice press quickly to force Arsenal back. On the second occasion Diop earns a free kick from Lacazette, along with Auba, will be frustrated at not seeing much of the ball in the last 20 minutes.
45 minCHANCE! West Ham's best opportunity of the half falls just before the interval as Rice gets above Mustafi but heads Anderson's corner wide of the far post. The academy graduate made good contact but couldn't direct his effort, and his wait for his first Premier League goal goes on.
1.20pmIt remains goalless at the break at the London Stadium, where the game has been open but equally scrappy. There have been chances for both teams but a lack of quality when it really matters. Arsenal will again have to rely on their second-half showing if they are to come away with three points today.
1.22pmArsenal started the better of the two teams and had a couple of chances through Lacazette, but West Ham certainly finished the stronger and probably should be 1-0 up at half time, with Rice squandering a great headed opportunity on the stroke of the interval. Anderson has also gone close for the hosts.
1.24pmPleasingly for Pellegrini, his new signing Nasri has been the standout player across both teams. The Frenchman is linking things up really nicely across their forward line in the way that the injured Manuel Lanzini does. If they can keep him motivated, Nasri could be a better signing than first thought.
1.26pmIwobi has picked up a lot of the same positions as Nasri but perhaps a little deeper in the pitch and that is why his combinations with Lacazette and Auba have not been as effective, especially later in that half. The Nigeria international does look like the one to make something happen for Arsenal though.
1.28pmMATCH STATS: The Irons shaded possession in that opening 45 minutes with 51% and had four corners compared to Arsenal's none. Their biggest shortfall so far has been their inability to seriously test Bernd Leno who was only had to make one save - from Mark Noble's tame shot.
1.30pmBENCH WATCH: Pellegrini will be pretty happy with how things are going so will likely keep Andy Carroll in reserve for a while longer. Ramsey might be one that Emery looks at to help Iwobi in creating chances as Aubameyang in particular has been starved of clear-cut chances so far.
46 minKICKOFF: We are back underway at the London Stadium, and there has been a change but not one made by either manager. Fourth official Stuart Atwell has been called up to run the line, with assistant referee Andy Halliday feeling unwell. Jonathan Moss is still the man in the middle, and he quickly shows the first yellow card of the game to Mustafi for bringing Anderson to ground with a late slide tackle.
48 minDeclan Rice had his head in his hands as he walked off for half time, having missed a great chance for an opening goal, but now he is wheeling away in celebration having opened his West Ham account. It is a really sharp finish from the midfielder, bending Nasri's layoff beyond a motionless Leno from 15 yards out after Arsenal had on several occasions failed to clear from a set piece.
50 minNervy moments in the West Ham defence minutes after taking the lead as a corner from Xhaka is flicked on at the near post but evades everybody else, when a runner at the far stick would have had a simple tap-in. Fabianski had come off his line and got nowhere near it.
52 minThe Hammers have won six of the nine league games in which they have taken the lead this season, although Arsenal are the kings of comebacks this season and did come from behind to beat Pellegrini's men in the reverse fixture. The visitors have a big task on their hands here though...
54 minSHOT! A poor pass out from Zabaleta gifts the ball to Guendouzi, who tries to place one from 20 yards out but sends his shot wide.
56 minA mesmerising dribble from Anderson sees him skip past three Arsenal defenders, and he stays on his feet under the challenge of Sokratis to win West Ham a corner. West Ham's fans stay on their feet too, to applaud the skill of their Italian winger.
58 minCHANCE! Lacazette gives away a cheap free kick, taking chunks out the back of Noble as he protected the ball on the right touchline. Anderson swings the set piece into the box and Ogbonna skews a header wide.
60 minSUBSTITUTIONS: Emery makes a double change, bringing on Ramsey and Torreira in place of Xhaka and Mustafi, which means a switch to a back four. No Premier League team has scored more goals through substitutes than Arsenal this season - 10.
62 minYELLOW CARD! Kolasinac will have more defensive responsibilities now he is in a customary left-back role. The Bosnian gets caught too high here, and is forced to bring down Antonio and accept his yellow card.
64 minCHANCE! Aubameyang has been quiet but has just had a couple of chances in as many minutes. Firstly the striker heads over a Ramsey cross which had him on the stretch, and then he has a much more suitable opportunity, blazing over the crossbar after being found by Kolasnic's infield pass.
66 minSHOT! Arsenal are starting to knock on the door now, with Ramsey's flick taking Rice out of the game and finding Iwobi for a left-footed drive which flashes past the post, with Fabianski scrambling in panic across his goal-line.
68 minSHOT! Guendouzi has another go from range but this is easy pickings for Fabianski. No doubt about it - Arsenal have upped the ante here and West Ham will need to be more resolute than ever before to keep them out, OR score a second on the break.
70 minSUBSTITUTION: Emery makes his final change, bringing on Bellerin for Maitland-Niles in search of more dynamism on the right.
72 minSUBSTITUTIONS: Pellegrini responds with a double change, replacing Nasri, who has been excellent, and Arnautovic with Snodgrass and Carroll. Arnautovic appears to wave goodbye to the London Stadium as he trudges off. West Ham's next home game is not for another month.
74 minCarroll's introduction will cause Arsenal's defence new problems and give West Ham a good outlet to hold up the ball and relieve pressure in the final 15 minutes, if the pattern of pressure from the visitors continues. Sokratis has already been called up for a couple of fouls trying to wrestle Carroll down to size.
76 minArsenal just haven't displayed their usual attacking sharpness so far today, which is strange considering the form that Aubameyang and Lacazette have been in this season. Ramsey has given them an extra attacking dimension, a midfield runner into the box but so far they haven't fashioned a chance for him.
78 minAnderson is not adored by the West Ham fans for his defensive work rate but the former Lazio winger has certainly done the dirty work today, and his backtracking here prevents Bellerin from getting a shot in. Along with Nasri who has gone off, Anderson and Rice have been the star performers.
80 minInto the last 10 minutes now and Arsenal are staring a second successive away defeat in the face. However, the Gunners have won eight points from losing positions with goals in the final 10 minutes this season.
82 minSUBSTITUTION: Pellegrini seems content to protect what he's got, replacing Antonio with a defensive midfielder in Pedro Obiang. That does take away much of West Ham's counter-attacking threat so they are relying on their defence from hereon in.
84 minDISALLOWED GOAL! Aubameyang has the ball in the net but the offside flag is up against both the goalscorer and provider Kolasinac, who had each strayed by several yards. The left flank remains Arsenal's most potent source of chances.
86 minThere does not appear to be any imminent danger to West Ham's lead, and in fact the hosts have had most of the ball in the last couple of minutes, and are still showing attacking ambition with Zabaleta getting forward on the overlap only to cross into the side-netting.
88 minCarroll has made a real nuisance of himself since coming on but has not had a chance yet. Snodgrass stands up a cross and it appears to be a mismatch of Carroll against Bellerin, but the Spaniard does well to usher the ball out for a goal kick.
90 minThere will be three minutes of stoppage time for West Ham to survive, and that starts with an Arsenal corner which Fabianski claims with authority. Both he and Nasri will be very pleased with their performances against their former club.
90+2 minZabaleta's clearance gives West Ham a bit of breathing space. Can Arsenal fashion one more chance?
90+3 minDISALLOWED GOAL! Koscielny buries a diving header superbly but the flag had gone up on Kolasinac, who was several yards offside, so much so that the finish from Arsenal's captain didn't even trigger mild celebrations from their fans.
2.28pmA huge victory for West Ham, who have now won six out of nine in the Premier League and climb to eighth in the table. It will be day that Declan Rice will never forget, with his maiden goal for his boyhood club earning them a first home win over Arsenal in 13 years. An off-day for the Gunners...
2.28pmA big victory for West Ham, and that is now six from nine in the league which sees them climb to eight in the table. It will be an afternoon to savour for Declan Rice, who scored his maiden goal for his boyhood club to earn them a first home win in 13 years over Arsenal, who had an off-day.
2.30pmThat's it from our coverage from the London Stadium. You can read our match report on the action here. Stay tuned with Sports Mole for live updates from Brighton vs. Liverpool. Thanks for joining me for this one. Until next time, goodbye!