Fellow substitute Marouane Fellaini made sure of the points with eight minutes left as United registered their third successive win.
Read below to see how the action unfolded at Old Trafford.
4.31pmHello, and welcome to Sports Mole's live coverage of the match in the Premier League between Manchester United and Leicester City.
4.34pmAfter one of the Manchester teams secured the most dramatic of wins earlier this afternoon, it is now the turn of the other to reclaim top spot in the Premier League. City were a tad fortunate to get the better of Bournemouth on the south coast, but United will be hoping to make lighter work of Leicester City at Old Trafford. After scoring eight times in their first two fixtures, expectations are high in the North-West.
4.37pmAs for Leicester, they make the trip to Manchester in pretty good spirits having responded from their opening-day defeat to Arsenal, but this will be far from a "nothing-to-lose" game for Craig Shakespeare. The Foxes boss knows that his players are fully capable of scoring goals against any side in the division and with it being unlikely that a clean sheet will be kept at United, the likes of Riyad Mahrez and Jamie Vardy will need to be at their best.
4.38pmAnyway, it's time for team news. Will Mourinho make any changes to a winning side? Will Shakespeare include Kelechi Iheanacho on the bench? Let's find out...
4.40pmMANCHESTER UNITED XI: De Gea, Valencia, Bailly, Jones, Blind, Matic, Pogba, Mata, Mkhitaryan, Martial, Lukaku
4.41pmMANCHESTER UNITED SUBSTITUTES: Romero, Darmian, Smalling, Herrera, Fellaini, Lingard, Rashford
4.41pmLEICESTER CITY XI: Schmeichel, Simpson, Morgan, Maguire, Fuchs, Mahrez, Ndidi, James, Albrighton, Okazaki, Vardy.
4.42pmLEICESTER CITY SUBSTITUTES: Hamer, Chilwell, Amartey, King, Gray, Iheanacho, Slimani
4.46pmI predicted in the preview for this match that Mourinho would not tinker with a winning team, but the Portuguese decides to make an alteration. In comes Anthony Martial - who has been in fantastic form off the bench - and he replaces Marcus Rashford. On the bench, Matteo Darmian is back to replace Victor Lindelof, who has still not featured for United in the Premier League.
4.49pmAs for Leicester, they are unchanged from the team which beat Brighton & Hove Albion last weekend. However, Kelechi Iheanacho is named among the replacements so the Foxes have Demarai Gray, Islam Slimani and the former Manchester City man all in reserve. Not bad, huh?
4.52pmThe full-time results are starting to come through and United are going to begin this match behind Huddersfield Town because the Terriers have claimed a goalless draw at home to Southampton. It's been some start from David Wagner's men!
4.56pmThere has only been five goals in the 3pm kickoffs but there has still been significant changes to the Premier League table. Click here to see where each club is currently sitting. United will return to the top of the standings with a point from this match.
4.59pmHEAD TO HEAD! Today's game represents the 115th meeting between the two sides, with United claiming 63 wins in comparison to 33 victories for Leicester. However, United have suffered just one defeat in 18 to the Foxes, with that game being the crazy 5-3 fixture at the King Power Stadium three years ago. United are also unbeaten in their last half-a-dozen outings against the Foxes.
5.03pmThe corresponding fixture last season ended in a 4-1 victory for United. Each of those two strikes were netted in the first half, with only a long-range consolation from Demarai Gray giving Leicester a little bit of respectability. Click here to read back on that fixture.
5.08pmWe could focus on any of United's attacking players, but we are going to take a closer look at Henrikh Mkhitaryan because while his teammates have been netting the goals, half of those efforts would not have come without his influence. The Armenian playmaker has four assists to his name from just 173 minutes of action. It's what United and Mourinho would have expected from him upon his arrival from Borussia Dortmund and although it has taken time to get the best of Mkhitaryan, he is certainly producing the goods now.
5.14pmLeicester are still likely to be active in the transfer market, but Shakespeare must be delighted with the impact of Harry Maguire, who was brought in from Hull City. His early performance for the Foxes - as well as his contribution for his former team - have earned him a call-up to the England squad, but it's games like this one where we will really see how good he is. Preventing Romelu Lukaku from scoring would be a considerable feather in his cap, but that is obviously a lot easier said than done!
5.18pmGoing back to Lukaku, it was announced earlier this week that Zlatan Ibrahimovic has re-signed for United and the legendary Swede is sure to put the Belgian under pressure later in the season. However, if Lukaku continues the form he has shown in the early weeks of his United career, can he keep Ibrahimovic on the bench.
5.22pmPREDICTION! We are looking forward to this one, simply because we think it is going to be a goalfest. However, we have to back United who will expect to score a few more goals in front of their own fans. Leicester need to get themselves through the early stages without conceding if they are to have a chance of a result. United to win 4-1.
5.27pmIt's time for the two teams to make their way out at Old Trafford. I don't remember atmospheres being like this last season. It's welcoming and expectant. There's a feel-good factor and a fear factor. That only spells trouble for the opposition.
1 minUnited get us underway.
3 minUnited have started well and truly on the front foot and Leicester are already coming under intense pressure. Crosses are coming from the right and Schmeichel only survives an iffy moment when coming to catch the ball when he is given a free kick.
4 minSHOT! It has been a positive reply from Leicester, with James curling a shot marginally wide of the far post from distance. De Gea had it covered if it had been on target.
7 minLeicester are actually starting to control possession and push United back now. It's highly impressive from Shakespeare's side who certainly aren't overawed.
10 minThere's been much talk of Mahrez's professionalism since effectively handing in a transfer request, and he has started this game well. I'm not so sure that he is going to get his move but that would be to Leicester's gain.
13 minIt looks like Ndidi has been given the responsibility to try to nullify Mkhitaryan, but the Armenian gets the better of his marker to drill a shot towards goal, only to see it partially blocked and deflect into Schmeichel's hands.
17 minMourinho is up off the bench. He's not happy with the tempo which United are playing at. Leicester look comfortable at the moment. They've certainly quietened the crowd down anyway.
18 minUnited have the ball in the net through Mata, who fires home the rebound after Lukaku's effort is well saved by Schmeichel. The assistant puts his flag up for offside, but Mata is level. Huge let-off for Leicester.
19 minCHANCE! United are fully on the offensive now. Martial's cross finds Pogba at the back post but on the stretch, he directs his volley wide of the far post.
20 minSAVE! It's all United and it only feels a matter of time. Mata controls the ball superbly inside the penalty area but his curler is tipped wide of the post by a sprawling Schmeichel.
23 minSHOT! Better from Leicester who give their defence a bit of a break. Vardy holds the ball up well before teeing up Okazaki, but the Japanese attacker's low shot is tame and De Gea is able to make the save.
24 minSHOT! Back come United through Pogba but after lining up a shot from around 25 yards out, the Frenchman drills his effort marginally wide of Schmeichel's right-hand post. We remain goalless but this is a hugely entertaining game.
29 minSHOTS! Pogba understandably has licence to shoot whenever he wants in and around the penalty area, but the midfielder is probably getting a little too desperate to get on the scoresheet. Twice in the space of about 60 seconds, he fires well off-target.
30 minSHOT! It's Martial's turn to try to open the scoring but despite a sharp turn on the edge of the penalty area, his low shot is well held by Schmeichel.
34 minAll of the pressure continues to come from United. I don't fancy Leicester's chances for seeing out the game without conceding a goal but for now, the rearguard action deserves credit.
35 minSHOT! Another Pogba shot which goes wide, but this is as close as he has come. His low strike from all of 30 yards just missed the post.
40 minWith five minutes to go in the first half, Leicester are still showing intent going forward whenever they can. It's risky strategy but equally refreshing. That said, Vardy has only been left to feed off scraps. The ball isn't really reaching him.
45 minThere will be one minute of added-on time.
45+1 minHALF TIME: Manchester United 0-0 Leicester City
6.18pmThe half-time whistle goes at Old Trafford and we remain goalless, despite United having created a hatful of chances. The home side should be ahead, however, with Mata seemingly onside when netting from close range. We predicted goals. We are still confident there will be some, but we haven't had any yet.
46 minLeicester get us back underway.
48 minIt's been a relatively quiet start to the second half, which suits Leicester rather than United. Lukaku nearly had a look in inside the penalty area but the Leicester backline were quick to clear the danger.
52 minPENALTY TO MANCHESTER UNITED!
53 minSAVE! United win a penalty after Simpson is adjudged to have handled a Martial cross, but Schmeichel makes a brilliant save to deny Lukaku to his right.
54 minBOOKING! Mkhitaryan is the first man into the book this afternoon after a cynical foul on Mahrez.
57 minSAVE! Mahrez looks the most likely to get a goal for Leicester and he almost nets from the narrowest of angles, only to see De Gea block well with his legs.
60 minSUBSTITUTIONS! Shakespeare makes the first move with a double change. Andy King and Demarai Gray are being introduced for Okazaki and Albrighton.
63 minUnited certainly aren't playing with the same swagger as the first half but they are still having the better of possession. Morgan and Maguire have been excellent at the back, but it only takes one mistake to change that.
64 minGray has just wasted a big chance for Leicester. Not with a shot, but to thread a ball through to Mahrez but not only did he wait too long, he over-hit his pass too.
66 minCHANCE! Mahrez has the ball on a string now. He is teasing Blind down the right flank and when he gets past his man here, the Algerian lashes a low ball across the six-yard box which evades everyone.
67 minSUBSTITUTION! A first alteration for United sees Marcus Rashford replace Mata.
70 minGOAL! Manchester United 1-0 Leicester City (Rashford)
70 minWhat an introduction. Mkhitaryan's corner finds the substitute on his own on the penalty spot, and the forward's volley goes into the net via Schmeichel's hands. The goalkeeper should probably do better. So should Vardy who needed to get closer to Rashford.
74 minSUBSTITUTION! A second change for United sees Marouane Fellaini come on for Mkhitaryan, who has provided his fifth assist of the season.
76 minSUBSTITUTION! Mourinho is definitely looking to close out the game rather than add a second. He withdraws Martial to replace him with Jesse Lingard.
77 minSUBSTITUTION! Now Leicester make their third and final change as Islam Slimani replaces Vardy. Interesting.
82 minGOAL! Manchester United 2-0 Leicester City (Fellaini)
82 minGame over and again, it is the substitutes who make a goalscoring contribution. Jesse Lingard remains patient on the ball inside the penalty area before his cross-shot picks out Fellaini, who diverts the ball into the net from six yards. There's a touch of offside about it, though. He is marginally level at best.
88 minTo their credit, Leicester are still pushing for a second, but this game is effectively over as a contest. United are going two points clear at the top of the table.
89 minBOOKING! James is booked by the referee after a trip on Rashford when he was in full flow.
90 minThere will be four minutes of added-on time.
90+3 minSAVE! This would only have been a consolation goal but Leicester should have halved the deficit. King met Gray's low cross but his close-range effort was kept out by the leg of De Gea.
90+5 minFULL TIME: Manchester United 2-0 Leicester City
7.26pmThe full-time whistle goes at Old Trafford and United have sealed a deserved 2-0 win over Leicester. It took substitutes Rashford and Fellaini to get the job done for the home side, but it highlighted United's strength-in-depth as they continue to set the pace at the top of the table. Leicester had their moments, but they were ultimately outclassed.
7.26pmThat will be all from Sports Mole for this match. Thank you for joining us this evening and we hope to see you again soon. Goodbye for now.