After an entertaining opening, Azpilicueta capitalised on a weak Carl Jenkinson header to slide the ball into the bottom corner from 10 yards.
Read below to see how the action unfolded at the Emirate Stadium.
6.46pmHello, and welcome to Sports Mole's live coverage of the Capital One Cup clash between Arsenal and Chelsea at the Emirates Stadium.
6.47pmWell this isn't a bad little encounter for a Tuesday evening, is it? The Premier League's top two will go at it in the last 16 of the League tonight, and with many changes expected, who knows what will happen?
6.49pmWe have yet to receive the official team news from the Emirates, but word is going around that six Chelsea players - Petr Cech, John Terry, Ashley Cole, Frank Lampard, Oscar and Andre Schurrle - have not made the trip to North London, but we will bring you news on that as and when we get it.
6.51pmWhile we wait for Chelsea lineup to reach us, how about I bring you the Arsenal one?
6.53pmARSENAL XI: Fabianski; Jenkinson, Vermaelen, Koscielny, Monreal; Ramsey, Wilshere, Rosicky, Cazorla, Miyaichi; Bendtner
6.55pmCHELSEA XI: Schwarzer; Azpilicueta, Cahill, Luiz, Bertrand; Mikel, Essien, De Bruyne, Mata, Willian; Eto'o
6.59pmFirst of all, let me run through the Arsenal team. Arsene Wenger has retained just three of the side that started against Crystal Palace on Saturday, with Jack Wilshere also included, despite playing for 82 minutes at Selhurst Park. There is also, of course, the inclusion of Nicklas Bendtner.
7.02pmAs for Chelsea, Jose Mourinho includes just one of the starting XI that played against Manchester City 48 hours ago, but why does he need to select more than one - that's an astonishing team for a so-called second-string side.
7.04pmARSENAL SUBSTITUTES: Viviano, Sagna, Hayden, Yennaris, Ozil, Giroud, Park
7.06pmCHELSEA SUBSTITUTES: Blackman, Ivanovic, Kalas, Ramires, Hazard, Torres, Ba
7.07pmThere is plenty of quality on both benches too. Who said the Capital One Cup didn't mean anything?
7.11pmBoth teams have only been required to win one match to reach this stage of the competition. Arsenal managed to come through on penalties against West Bromwich Albion, while Chelsea coasted to victory away at League One outfit Swindon Town.
7.17pmBoth Wenger and Mourinho have placed trust in a couple of strikers that are under pressure to perform. It was expected that Nicklas Bendtner would be leaving the Emirates during the summer, but the Dane was forced to remain in North London after Wenger failed to add to his striking department. It left Bendtner in a tricky situation after a couple of disappointing years in front of goal, but he has been handed the perfect opportunity to win round the Arsenal supporters this evening.
7.20pmIt has been well documented that Samuel Eto'o has looked a shadow of his former self since arriving at Stamford Bridge. After a slow start, he netted a fine goal against Cardiff City, but since opening his account, he has played just 15 minutes. Will tonight be the night that the Cameroonian displays his talent in attack?
7.24pmThis London derby isn't the only Capital One Cup match that you can follow with Sports Mole this evening. We also have live coverage of Norwich City's trip to Manchester United, and keep an eye out for updates on the three other ties that are taking place tonight.
7.29pmPREDICTION! This is a difficult one to call. Arsenal have the home advantage and plenty of momentum at the moment, but Chelsea appear to possess the stronger team tonight. Chelsea to win after extra-time.
7.32pmThere is less than 15 minutes remaining until kickoff at the Emirates. The Gunners have reduced ticket prices to £10 for this match, so you would expected a decent crowd at the Emirates.
7.37pmWhen it was announced that Chelsea had to play just 48 hours after the Manchester City match, Jose Mourinho soon voiced his displeasure at the decision. It makes you wonder when he could select a side like the one he has done.
7.42pmThe two teams are heading out onto the pitch in North London. Michael Essien will captain Chelsea in the absence of John Terry, Frank Lampard and Petr Cech.
7.45pmArsene Wenger and Jose Mourinho have just shared a handshake. Mourinho tried some small-talk, but I think Wenger just wanted to get to his seat.
0 minChelsea get us underway, and immediately win a corner.
2 minThe first one from the right is cleared, but they quickly win a second. However, that one is clear as well. Arsenal can't get hold of the ball at the moment.
4 minA David Luiz mistake allows Ryo Miyaichi to break down the right-hand side, but his cross is hoofed away by Cahill. There is already an openness to this game that suggests that we are in for a few goals.
6 minSome crisp passing from Chelsea sees Mata pick up the ball around 30 yards out. He attempts a give-and-go with Eto'o, but he is quickly closed down by the Arsenal defence.
9 minChelsea have had 75% of possession during the opening nine minutes. That's a phenomenal stat for a visiting side at the Emirates. Arsenal win the ball in midfield, but Bendtner's volley is blocked by Cahill.
11 minKevin de Bruyne cuts inside from the right before setting up Willian, but the Brazilian's shot is deflected wide for a corner, which, like the first two, was easily cleared.
14 minIt will be a welcome sight for any Chelsea fan to see Michael Essien making a lung-busting run from midfield, but it is evident that he doesn't have the pace of a few years ago. Arsenal dispossess him, and break forward to earn a corner, which is headed clear by Eto'o.
19 minSHOT! There is a fantastic tempo to this match, with plenty of challenges going in from both sides. Chelsea dispossess Arsenal and break up the other end, with De Bruyne curling the ball straight at Fabianski from 20 yards.
22 minMore good play from Chelsea sees Bertrand cross from Eto'o at the near post, but the former Barcelona man flicks the ball well wide of the post. It's been a quiet start from the 32-year-old.
25 minGOAL! Arsenal 0-1 Chelsea (Azpilicueta)
25 minYes, you read correctly...Azpilicueta, of all people, has given Chelsea the lead! It was a similar goal to that of Torres on Sunday. There was a mix-up between Wilshere and Jenkinson, and Azpilicueta latched onto Jenkinson's weak header to slide the ball past Fabianski from 10 yards.
28 minIf any of you had a bet on Azpilicueta to be the first scorer, I salute you.
29 minBOOKING! Mikel has been booked for attempting to cynically scythe down Wilshere.
30 minCHANCE! Azpilicueta loses out to Monreal on the right-hand side, and the Arsenal left-back advanced into the penalty area before firing a low drive marginally past the post.
33 minMonreal whips in a cross towards the penalty spot, which Essien miscues for a corner. Cazorla curls the ball into the box, but it is easily claimed by Mark Schwarzer.
35 minYou can see how desperate Eto'o is for a goal. His approach-play and strength is impressive, but he swings a left foot at the ball from 25 yards, and it balloons skywards before going for a throw-in.
38 minThere's less than 10 minutes to go before the break. In the other games, Manchester United lead Norwich City thanks to a penalty from Javier Hernandez, while Fulham hold the advantage over Leicester City.
41 minAre Samuel Eto'o and Michael Essien competing for worst shot of the season? The ball is passed into the path of the Ghanaian, but he badly slices the ball and it spins out for another throw-in.
45 minThere will be one minute of added-on time.
45+1 minHALF TIME: Arsenal 0-1 Chelsea
8.33pmIt has been a first half lacking in clear chances at the Emirates Stadium, but there has been plenty of quality on the ball. Chelsea probably deserve their advantage, given to them by an opportunistic effort from Cesar Azpilicueta, but Arsenal are by no means second best in this contest.
8.36pmChelsea are leading on both the shots and possession count. The Blues have had eight efforts compared to Arsenal's four, while the West-Londoners have had 55% of the ball.
8.40pmBefore the restart, I should remind you that if we are level at 90 minutes, we will go into extra-time. I doubt that is something that either team wants, but you'd have to say that it has a fair chance of happening.
46 minEveryone has returned for the second half. It will be Arsenal to get us back underway.
48 minMesut Ozil and Olivier Giroud are already out warming-up. Could that be a sign of things to come?
50 minSHOT! Eto'o has began the second half looking eager to get hold of the ball, and after collecting it on the left, he cut inside on his right foot to drive a shot on goal, but his 20-yard effort just missed the post. Much better though.
52 minSHOT! It's Cazorla's turn to try his luck from distance, but his shot goes a couple of yards wide of Schwarzer's goal. Chelsea are about to make a substitution.
55 minArsenal are having a sustained period of possession, which is keeping Chelsea on the back foot. A mistake from Luiz allows the Gunners in, but they over-play the situation and Schwarzer claims.
56 minDoesn't look like that substitution is happening now. Ivanovic had been all set to replace Cahill, who appeared to be suffering with cramp.
60 minSome of the possession-football in this game has been outstanding, even if the final delivery hasn't. We have reached the hour-mark, and this tie could still go either way.
62 minSHOT! Aaron Ramsey has once again been terrific tonight, and he lets a shot go from 20 yards that just misses the bottom corner.
63 minSUBSTITUTION! Wenger has seen enough, and has opted to bring on one of his "big guns". Mesut Ozil is on for Ryo Miyaichi.
66 minGOAL! Arsenal 0-2 Chelsea (Mata)
66 minOh my, what a strike from Juan Mata! On his weaker foot too. The ball bounces off Willian's head into the path of the Spaniard, who lets rip with a swerving effort from 20 yards that flies past Fabianski and into the top corner.
67 minSUBSTITUTION! Wenger immediately withdraws Bendtner for Giroud. Can the Frenchman help save this game for his side?
69 minSUBSTITUTION! Mourinho responds by replacing De Bruyne with Ramires. 20 minutes to go.
71 minSHOT! Some strong running from Wilshere helps create a chance for Giroud, but his instinctive effort is blocked by the advancing Schwarzer. However, Arsenal have a free kick in a threatening position, but Koscielny's header goes wide.
72 minCLOSE! A quick-fire break from Chelsea starts with Azpilicueta passing to Essien. The Ghanaian plays a first-time ball to Ramires, who gets to the byline, but his cross is prevented from reaching Eto'o by Koscielny.
74 minBOOKING! Another Chelsea break is halted after Mata loses the ball in midfield, and Essien is forced to haul down Wilshere, which deservedly warrants a booking.
77 minEFFORT! The quality has significantly risen since the arrival of Ozil, and good work from the German allows Wilshere to receive the ball in space, but he strikes it over the bar from 20 yards. Should have done better.
81 minSUBSTITUTION! This is quite a sight. A few of the Chelsea players that haven't featured that often regularly - Azpilicueta, Luiz and Eto'o - have all gone down with cramp! One of those, Eto'o, is being replaced by Demba Ba.
85 minI think Mourinho gives this latest decision! Ba and Vermaelen are competing for a high ball, and the Belgian pushes the striker. The referee hadn't blown the whistle, but Mourinho was almost on the pitch collecting the ball! Bizarre.
89 minTime is almost up at the Emirates. It looks as though Chelsea are going to qualify for the quarter-finals.
90 minSHOT! I nearly spoke too soon. Cazorla does brilliantly to engineer a shooting opportunity, but he drags his shot wide of the mark. There will be four minutes of added-on time.
90+1 minEFFORT! Ramires nearly puts the icing on the cake for Chelsea. He seemed to be eyeing up his shot for an eternity, and when he did finally strike the ball, it deflected onto the top of the net.
90+3 minVermaelen is adjudged to have brought down Ba when the striker was clear on goal, but it wasn't deliberate. Mourinho makes his final alteration, bringing on Kalas for his Chelsea debut.
90+4 minFULL TIME: Arsenal 0-2 Chelsea
9.36pmPhil Dowd blows the full-time whistle, and Chelsea have beaten Arsenal to progress through to the last-eight of the Capital One Cup. That was as professional as it gets from the Blues.
9.38pmArsenal attempted to launch a second-half fightback, but their final ball wasn't there tonight, and Nicklas Bendtner may as well have not been there in attack...
9.40pmThat will be all from Sports Mole this evening. Thank you for joining us for what has been a quality cup tie between two fantastic sides. Goodbye for now.