The Belgian broke 64 minutes of deadlock mere seconds after his introduction from the bench, pouncing on a spill from Martin Dubravka to poke home from close range.
Newcastle had wasted a series of first-half chances to take the lead through Christian Atsu and Salomon Rondon but were not as much of a threat after falling behind.
Marcus Rashford made the points safe 10 minutes from time to secure the Red Devils a fourth successive Premier League win under interim manager Ole Gunnar Solskjaer.
Relive all of the action from Tyneside with Sports Mole's minute-by-minute updates below.
The year is now 2019, but Manchester United fans could be forgiven for thinking it was 1999 again. They are back to winning games, scoring goals and singing Ole Gunnar Solskjaer's name, and they enter the New Year with a renewed sense of optimism. Their first pit stop of 2019 is a trip to St James' Park to face Newcastle United...
Marcus Rashford is passed fit for the Red Devils despite limping off late on during Sunday's 4-1 win over Bournemouth. The England international again leads the Manchester United line with Romelu Lukaku, a scorer as a substitute against the Cherries, a handy centre forward to have in reserve.
Alexis Sanchez is also named on the bench after six weeks out with a hamstring injury. The Chilean has not scored for United since grabbing a last minute winner in a 3-2 victory against Newcastle in October's reverse fixture at Old Trafford. Can Solskjaer have the same rousing impact on the Chilean as he has United's other attackers?
Solskjaer makes three changes from the Bournemouth game, replacing the suspended Eric Bailly with Phil Jones and bringing in Juan Mata and Antonio Valencia in place of Jesse Lingard and Ashley Young. Paul Pogba and Anthony Martial will be hoping to continue their sparkling form.
Newcastle manager Rafael Benitez makes just the one change from their 1-1 draw with Watford four days ago, with Federico Fernandez missing with a hip injury and deputised by Fabian Schar at centre-back. Florian Lejeune is back from a long-term layoff to provide defensive depth on the bench.
Ki Sung-yeung is away at the Asia Cup with South Korea so Isaac Hayden gets another opportunity in central midfield. The one-time Arsenal youngster has only made four Premier League starts this season, but his partner Mohamed Diame is Newcastle's only outfield player to start all of their top-flight matches this term.
Salomon Rondon has five Premier League goals in his last eight starts, finally providing Newcastle with a reasonable goal threat up front that they have been missing since returning to the top flight two years ago. Christian Atsu gets the nod over Kenedy as one of the supply lines to the South American.
Three games, three wins and 12 goals scored, it has been the perfect start for Solskjaer, who is aiming to become only the second manager in United's history to win his first four league games in charge, emulating Matt Busby in 1946. He has enjoyed a friendly start fixtures wise but the early signs are promising both results and style wise.
One of the biggest impacts of Solskjaer's arrival has been the renaissance of Paul Pogba. The Frenchman has been directly involved in seven goals in three league matches under Solskjær, scoring four and setting up three, compared to six goal contributions - three goals three assists - in 14 league appearances under Jose Mourinho this season.
Pogba's return to form can only really be attributed to confidence. He is playing with most of the same players, and in a very similar system to that which he was under Mourinho, but has clearly been given the freedom to express himself outside of stricter tactical instructions. And Solskjaer is not the only manager to give the midfielder their backing...
Should Pogba inspire another vintage United offensive display, the Red Devils could score three goals or more in four consecutive league fixtures for the first time since August to September 2011. The World Cup winner has not transformed United's attack alone though - Rashford, Martial and Lingard have combined for five goals and four assists in three games.
While United fans will be delighted with the attacking football that their team are playing post-Mourinho, the change of manager has not improved their defensive fortunes as yet. The Red Devils have had defensive slip ups in each of Solskjaer's three matches, and have kept just two Premier League clean sheets this season, a joint-low with Fulham.
A major source of United's defensive pain this campaign has been set pieces, from which they have conceded 14 league goals, including in each of the last three games. Tonight's opponents Newcastle have the division's next worst record, letting in 12 goals from dead-ball situations, so corners and free kicks could be interesting this evening!
Solskjaer will have mixed memories from his playing encounters with Newcastle. The Norwegian scored four goals for United against the Magpies, but also played in 1996's famous 5-0 defeat, and was shown his only Premier League red card at St James' two years later for this ultimate 'team tackle' on Rob Lee. It is not often a sent off player receives a standing ovation!
The 45-year-old's managerial history against Newcastle is also as much bad as it is good. A 2-1 win for Cardiff City in the FA Cup third round in January 2014 was his first competitive match as a manager in English football, but a 3-0 loss on Tyneside that May saw the Bluebirds relegated from the top flight, and he was sacked four months later.
Rafael Benitez continues to be quite pragmatic, publicly at least, about Newcastle's chances of avoiding relegation. He told BBC Sport this week: "The target will be at the end of January if we are out of the bottom three, then that will be good news." The Magpies are currently 15th in the table despite winning just one of their last seven.
The Toon Army are known for their passionate support and have found a manager that they adore, but that has not been translated into positive home results this season. Newcastle have already lost seven league games at St James' in 2018-19, a joint-high with Huddersfield - they have only twice lost more Premier League home fixtures across an entire season.
Only bottom-of-the-table Huddersfield have scored fewer than Newcastle's 15 league goals this campaign. Ten of those 15 have been scored in the opening 30 minutes of their matches, with four second-half strikes the joint-fewest in the division. Maybe if Rafa would have taken more second-half risks, a couple of their six draws would have been turned into wins?
Benitez has been very consistent in his cautious approach to matches against the Premier League's elite in recent times, despite taking heavy criticism from pundits for negative tactics. Well, he may want to consider changing tact as Newcastle have been beaten in all eight fixtures this season against the sides who began 2019 in the top eight of the table.
However, the shrewd Spaniard knows how to get the job done against Man United, winning each of his past four home games against the Red Devils in all competitions: two with Liverpool, and one each with Chelsea and Newcastle.
HEAD-TO-HEAD: Last season's win over United at St James' Park, courtesy of Matt Ritchie's strike, was Newcastle's only success over the last eight encounters. Tonight, the Magpies could earn consecutive top-flight home victories against United for the first time since 1987.
Just over 10 minutes until kickoff here on Tyneside. Four of tonight's other five Premier League games have already kicked off, including Chelsea's visit of Southampton to Stamford Bridge which you can follow with my colleague Darren Plant here. Bournemouth vs. Watford has been delayed until 8pm.
AS IT STANDS: Three wins in a row has made United's top-four prospects look a little rosier. Victory this evening could take them to within five points of Chelsea in fourth, although the Blues have a very winnable match, at home to Southampton as just discussed. Three points for Newcastle would lift them a place to 14th but I'm sure Rafa would settle for one.
According to BBC Sport, Solskjaer has already confirmed that we will see Sanchez on the pitch at St James' Park at some point tonight, in order to get some match action into his legs. He is quoted as saying: "He will be involved [at Newcastle], yes. He wants to play all the time, he's one of those characters. He has not had enough fitness work but he is champing at the bit."
This fixture has served up some Premier League classics over the years, and that is because it is usually a guarantee of goals. Forty have been scored in the last 12 top-flight encounters, 27 of those by United, and we know from recent weeks that the Red Devils have found their shooting boots once more!
United have made quick starts in each of their three matches under Solskjaer, taking the lead inside half an hour on all three occasions, twice inside the opening five minutes. That is something Newcastle will need to be very wary of as an early goal conceded would throw Rafa's game-plan out of the window.
PREDICTION: Solskjaer's United have a lot of goals in them and I cannot see Newcastle either containing or outscoring their visitors tonight. I am expecting another free-scoring United victory by a scoreline of 3-1.
Newcastle have lined up a little differently than we expected, with Benitez returning to the back five that he has used at times this season. That means Dummett is on the left side of the central three, with Ritchie operating as a wing-back. He gives the hosts the flexibility to change system mid-game.
It has been a decent start from United, who are passing the ball quickly through midfield and clearly looking to move it forward at every attempt. An attempted one-two between Mata and Martial inside the area doesn't quite pay-off, with the loose ball falling to Pogba whose shot is held by Dubravka.
This is Antonio Valencia's first Premier League appearance for United in three months, and yet the Ecuadorian wears the captain's armband tonight. Valencia has made three Champions League appearances during this period but has been firmly out in the cold. Solskjaer has not risked ruffling any feathers by changing the captain's heirarchy - Mourinho caused a stir in doing so and making Pogba skipper earlier this season.
SHOT! Perez barges into Martial on the inside left to gift United a free kick, and the visitors load the box as Jones and Lindelof come forward. However, Rashford tries to catch Dubravka out by sneaking a shot in at the near post from 30 yards, but the consistent Newcastle stopper is alert to the danger.
Lascelles takes a risk by taking out Rashford during a penalty-area 50-50 that was definitely more than shoulder-to-shoulder. That was a classic 'let him know you're there early' tackle but could have been costly as he knocked Rashford to ground without taking much of the ball at all.
SHOT! Two decent half-chances for Newcastle, both created nicely but finished weakly by Atsu. Firstly, the winger beautifully brings down a ball over the top from Schar, but his left-footed effort is held by De Gea, who is not troubled by Atsu's right moments later after he cut inside Lindelof and fired away.
CHANCE! It has been a nervy few moments in the United defence, with Jones the main culprit. A shocking error from the England international gifts the ball to Rondon one-on-one, but Jones just about manages to recover and make a last-ditch sliding challenge. Rondon seemed to hesitate, looking for the offside flag.
Martial is starting to get into the game and has had a couple of dangerous looking breaks down the left flank. Dubravka had a shot that went into the side-netting covered, and next time Martial tried to pick out Pogba who had made a run to the back post, but Lascelles intercepted on the six-yard line.
Atsu is certainly looking like the danger-man for Newcastle when they counter-attack. Perez finds the Ghana international with an early spread of the ball and because he is forced wide by Lindelof the angle is against him when he screws a cross-cum-shot harmlessly across the face of goal.
LATEST: No goals so far at St James', but there has been a big one at the bottom of the table that may interest Newcastle, with Huddersfield taking the lead against Burnley. Watford are also in front away at Bournemouth thanks to a strike from skipper Troy Deeney.
Both teams are focussing most of their attacking play down their respective left sides, which is starting to make the game more stretched than Newcastle woud like as the ball is being spread from side to side.
CLOSE! Two sights of goal in as many minutes for United, with Rashford nearly capitalising on miscommunication in the United backline, only for Dubravka to just about beat him to the loose ball on the edge of the box. Moments later the United striker exchanges a one-two with Martial whose deflected shot has Dubravka beaten but lands on the roof of the net.
For possibly the first time in the match, United have the numbers on Newcastle in attack but they don't make the most of it as Pogba's attempted cross to Mata at the back stick is headed clear by Dummett.
YELLOW CARD! Lascelles got the benefit of the doubt from referee Marriner earlier, but does not get away with this late tackle on Herrera which costs him a booking. The defender overran the ball bringing it out of defence and caught Herrera on the ankle as he tried to make amends.
SHOT! Pogba works some space for a shot on the edge of the box - a very similar position to which he scored one of his double against Huddersfield - but he drags this effort a few yards wide to the right.
Dubravka again sweeps up the mess in his defence by darting out of his goal to thwart Mata, who was running on to a Lascelles tackle on Rashford which had deflected perfectly into his path. Very alert goalkeeping from Newcastle's number one who is proving to be excellent signing.
CHANCE! It has been 10 minutes or so since we have seen anything from Newcastle as an attacking force, but they haven't gone into their shell completely. Yedlin makes a good overlapping run and hangs a cross up for Rondon, who has the beating of Lindelof in the air but can't keep his header down.
LATEST: Southampton could potentially do United a favour tonight as they are holding Chelsea 0-0 at half time at Stamford Bridge. It is also goalless between West Ham and Brighton and Wolves and Crystal Palace. Watford now lead Bournemouth 2-1 while Burnley are back level with Huddersfield at 1-1.
There is a stoppage at St James' as Martial receives treatment after taking a ball to the face at point-blank range from Perez. They can be sore ones in this temperature as the Frenchman can testify!
Mata swings in a free kick from the right which Jones gets his head to, but the twin pressure from Diame and Rondon makes it difficult for the United defender to direct his header and it goes over.
Another stoppage here caused by a knock to Atsu, who has had a fading influence on the half after a really bright opening 20 minutes. His pace has proved to be a good outlet on the break though so Benitez will hope that he can run it off.
United are on the front foot as we approach the break, with the Magpies now sitting 10 men behind the ball in the aim of getting to the half-time checkpoint. They have defended well and had a method of getting at United's defence themselves. It has been a good performance thus far, minus the end product.
The physio is on again, this time to tend to Diame who is on the floor and holding his groin. This busy festive period can cause a lot of injuries but I suspect Newcastle are just trying to wind the clock down and get to half time. There is two minutes of stoppage time for them to get through unscathed.
United are not having it as easy at St James' this evening, with Newcastle proving typically resolute and also having their fair share of chances. Solskjaer has some thinking to do at half time. Can he bring himself on?!
The Magpies had a really good spell from minutes 10 to 20 when they created two or three decent chances, and they may be ahead at the interval had Atsu showed a bit more conviction with his finishing. Jones will be relieved that it remains deadlocked after his mistake went unpunished by Rondon.
While they have not had the success they have had in previous matches, United do still look sharp going forward and are testing Newcastle's defence with one-touch passing and quick movement around the box. But Newcastle's defence have been up to that test, with Lascelles putting in a captain's display.
LATEST: Not for the first time this season, the Vitality Stadium is the place to be for entertainment - it is 3-3 between Bournemouth and Watford at half time! All six of tonight's Premier League games are currently level - four at 0-0 while Burnley have pegged back Huddersfield through Chris Wood.
BENCH WATCH: Solskjaer has promised us Sanchez at some point, and he also has Lingard and Lukaku at his disposal so plenty of firepower in reserve. If Diame's stoppage-time injury is legitimate, Benitez may have to turn to Shelvey and he is a very different type of midfielder, capable of creating something with his passing but he could leave Newcastle more open.
YELLOW CARD! Lindelof is shown a yellow card - his first of the season - for deliberate handball after using his hand to control the ball. The Swede claims he was pushed by Rondon but referee Marriner didn't see it that way.
A feature of United's new approach under Solskjaer that has not been as evident tonight is the full-backs getting forward. Shaw seems determined to change that in the second half and has made a couple of adventurous runs.
Lindelof wins a 50-50 with Rondon in the Newcastle half and quickly releases Rashford who is played onside by Schar. Lindelof continued his run into the box, and there was also Pogba and Martial to aim at but Rashford selfishly shot on his left foot from a tight angle, out for a throw-in on the far side.
SUBSTITUTION: Diame has been unable to run off his first-half injury and so Shelvey is on for the Magpies. Benitez may be forced into another change too with Schar taking his turn to receive treatment.
Schar is okay to continue and Rashford welcomes him back to the action by barging him straight into the advertising hoardings. No complaints from the Swiss international as United's frustrations start to show.
Atsu is becoming a major player in this game again, but it is the same old story with his finishing. Schar makes an interception and strides out with the ball before shifting it on to the winger, who runs at the United defence who back off and invite a 20-yard shot which goes wide of De Gea's post.
Shelvey has brought St James' to life with two pieces of play, the first of which is an outstanding outside-of-the-foot pass between Jones and Shaw. Perez can't bring it under control instantly and that allows Shaw to make a block. Shelvey then shoots low and hard into De Gea's gloves from 25 yards.
SUBSTITUTIONS: Solskjaer turns to his multi-million pound bench and calls upon Lukaku and Sanchez, with Martial and Mata making way. Can they find a way to unlock this Newcastle defence?
Talk about an instant impact! Mere seconds after coming off the bench, Lukaku puts United ahead, pouncing on the rebound of Rashford's driven free kick - spilled by Dubravka - to poke home from a few yards out. I'm not sure of the exact timings but that has to be close to a Premier League record for quickest goal by a substitute!
Dubravka has been Newcastle's standout player this season but that was a definite error from the goalkeeper. He tried his best to make amends by jumping on the second ball, taking a kick on the hand in the process, but Lukaku just beat him to it. Can Newcastle respond? They have only scored four second-half goals all season, remember.
Shelvey shifts the ball around Herrera to engineer a shooting chance for himself but loses control of the ball and slices it horribly wide. For someone with such good technique, it has always baffled me that he doesn't score more goals.
Rondon cannot show the same level of reactions as Lukaku did at the other end as the ball bounces his way in the box and he fails to bring it under control. Had he been able to, De Gea may have been stranded as he had come rushing out himself to claim the ball.
We've seen the good side of Shelvey since his introduction, and now the bad side. The midfielder leaves a bit in on Pogba during a 50-50, going in with his studs, and he is lucky that the Frenchman didn't make more of it otherwise he could have been in trouble.
United have a second and that could be enough to see off Newcastle! Rashford is the scorer, slotting the ball beyond Dubravka from 12 yards out after being found by an Alexis Sanchez pass during a swift break which left the hosts short at the back. That is three goals in four starts under Solskjaer for Rashford!
RESULT! Southampton have held Chelsea to a 0-0 draw at Stamford Bridge, which would make this an even better result for United as they would close the gap on the fourth-place Blues to six points.
SUBSTITUTION: Solskjaer's changes have worked a treat tonight, and he makes his final one here as he swaps Rashford for Lingard. Herrera has been in the wars in the last couple of minutes but they must be confident he can continue.
Newcastle have had their chances tonight - most of which have fallen to Christian Atsu - and this game could have finished very differently had they taken any of those first-half opportunities. They are not lacking triers but need more quality. Will Rafael Benitez get any funds in January to get that?
There will be six minutes of stoppage time here due to the various injury breaks, the latest of which has seen DeAndre Yedlin pull up, which will be a concern considering his importance to the Newcastle cause. What is worse for Newcastle, is Benitez is made all of his subs.
CHANCE! Pogba should have added a flourish to the scoreline, rounding Dubravka at the end of a quick counter but shooting into the side-netting with an open goal to aim at 15 yards out, albeit from a tricky angle.
Manchester United go marching on under Ole Gunnar Solskjaer, making it four wins from four with victory over Newcastle tonight thanks to second-half goals from Romelu Lukaku and Marcus Rashford. Newcastle had their chances in the first half and were made to rue those missed opportunities.
That's it from our coverage from St James' Park. You can read our match report on the action here, and catch up on the rest of tonight's Premier League scores here. Thanks for joining us tonight, and remember to return to Sports Mole tomorrow for minute-by-minute updates of the big title clash between Manchester City and Liverpool. Until then, goodbye!
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