The skipper broke the deadlock early on, with Robin van Persie making it 2-0 soon after. Diafra Sakho reduced the arrears before the break, but despite their numerical advantage after Rooney had seen red for kicking out at Stewart Downing, the Hammers couldn't turn their domination into another goal.
You can find out how the match unfolded with Sports Mole's text updates below.
2.03pmAfternoon all. One thing is surely certain from this game involving Manchester United and West Ham United - goals! Both teams are exciting going forward, but neither is watertight defensively. It should make for an entertaining clash at Old Trafford so let's hope that it doesn't disappoint.
2.05pmLet's begin with a look at the two teams, starting with hosting United, who have have a couple of debutants in defence...
2.06pmMAN UNITED XI: De Gea; Rafael, McNair, Rojo, Shaw; Blind, Herrera, Di Maria, Rooney; Van Persie, Falcao
2.07pmMAN UNITED SUBS: Lindegaard, Thorpe, Fletcher, Pereira, Valencia, Mata, Januzaj
2.10pmWhat a huge afternoon it is for young Paddy McNair. Aged just 19 and with no previous experience of the senior setup, he appears for United for the first time. He will play at centre-back alongside Marcos Rojo, with Jonny Evans, Chris Smalling, Phil Jones and Tyler Blackett all unavailable. There is also a first outing for summer signing Luke Shaw at left-back, while Robin van Persie, Radamel Falcao, Wayne Rooney and Angel di Maria all retain their places.
2.18pmThe big news for West Ham is that midfielder Mark Noble does not feature at all - one can only assume that he has picked up an injury. Cheikhou Kouyate is also not available, which has seen Diego Poyet come into the midfield to partner Barcelona loanee Alex Song. Aside from that, the team is the same from the one that defeated Liverpool last time out, with Enner Valencia and Diafra Sakho continuing as the centre-forward pairing.
2.21pmObviously the unpredictability of United makes them the headline news here, but West Ham full-back Guy Demel has just been talking to Sky Sports News. Here is some of what he had to say:
"It's never easy coming to Old Trafford and we know it's going to be a hard afternoon for us. But we feel we can cause them problems. You can see that the Liverpool game was key for us and we want to continue to try to play that brand of football and be successful."
2.24pmSo, Demel believes that West Ham can cause United problems today and it's easy to understand why, particularly if you watched their clash at Leicester last weekend. The Foxes scored five times and but for some wayward finishing in the closing stages, they could have won by an even bigger margin than two goals. What's more, at a time when United's rearguard is in desperate need of some experience, Louis van Gaal has had to turn to a untried and untested 19-year-old.
2.28pmWhat do we know about McNair, then? Well, this might make some of you feel old, but when he was born, Take That topped the charts with Back for Good. The defender moved to United at the age of 16 and recently made his debut for Northern Ireland Under-21s. He also scored a header for a Man United XI during a pre-season friendly in the summer, which you can watch below:
2.31pmI should point out, United also have another young defender on the bench in the form of Tom Thorpe. At the age of 21 and having played some senior football while on loan with Birmingham City last season, it's a little bit of a surprise that he doesn't start ahead of McNair. Van Gaal obviously rates the Northern Irishman.
2.35pmVIDEO! Right, with around 25 minutes to go until we get underway at Old Trafford, why not see how Sports Mole's very own Matt Law, Barney Corkhill and Pascal Lemesre see this encounter panning out:
2.40pmElsewhere, United supporters will be happy to learn that a stunning goal from Phil Jagielka has secured a 1-1 draw for Everton away at rivals Liverpool in the Premier League's early clash. You can read Sports Mole's match report from Anfield here.
2.44pmPREDICTION: The chaps have had their say below, but I'll throw my hat into the ring as well. United's problems at the back are well documented, but it's so hard to ignore the talent that they have going forward. At Old Trafford, you would expect them to win more than they don't. Having said that, West Ham have players that can cause damage. Let's go for 3-1 to hosts, with Falcao opening his United account.
2.46pmIt would seem that myself and former United full-back Phil Neville are on similar wavelengths, which is slightly concerning:
2.49pmBefore this match gets started, let's quickly take a look at what the two managers have been saying coming into this encounter. It would seem that Allardyce would be happy if his side collected just a point:
"They will be pretty down about that performance they gave at Leicester. I'm thinking [it will be] a backlash. I think that because of the determination of the Manchester United players and the fact they are playing at Old Trafford.
"They will be hurting and they know the only way they can put that right is to get out onto the field and punish us for it - so we will have to be careful about that. A draw would be great for me. Anything more than a draw would be outstanding as far as I'm concerned."
2.51pmMeanwhile, here are Van Gaal's thoughts: "I hope we play better as a team [than against Leicester] - not especially when we're in possession but when we lose the ball. We have to do a lot better [on that aspect] than we did against Leicester.
"West Ham are maybe the best team we've had to face until now. I was very impressed [with their performance against Liverpool] and they play with the same system as we do at this time. More or less, it will be system against system. I hope we shall give our best and the fans can enjoy a victory again."
2.54pmHere are some images of McNair warming up. How nervous will the youngster be right about now?!
2.57pmThe players are now making their way out on to pitch and the handshakes are taking place. Only a couple of minutes until we are off and running.
1 minKICKOFF! The visiting Hammers, attacking from right to left in the first half, get proceedings underway at Old Trafford.
2 minCHANCE! What a huge opportunity for Falcao to break his United duck. Rooney's free kick from the left flank is dangerous, but as his Colombian teammate tries to make contact, he cannot quite reach and the ball rolls behind for a goal kick. Any sort of touch on the ball and it surely would have been a goal.
3 minBOOKING! Something has upset Alex Song! He brought down Di Maria within the opening 30 seconds and has now just booted the Argentine off the ball. He is rightly cautioned and will be walking a tightrope for the remainder of the encounter.
5 minIt's a captain's goal from Rooney, but a lot of the credit has to go to full-back Rafael. He skips away from Cresswell and sprints down the right touchline. The Brazilian then picks out Rooney, who with the ball bouncing up inside the area, cushions a great shot across Adrian into the far corner of the net. That is some finish from the Englishman and United lead.
7 minCHANCE! If Valencia had shown Rooney's composure, West Ham would be level. He scampers beyond the United defence and is onside, but his shot from inside the area is wild and flies over the crossbar. From 10 yards out, he should be doing much better with that.
10 minAnother opening for United as Rooney floats a cross towards the back post. It seems that Van Persie is going to have a simple headed chance, but Cresswell does well to ease him out and the ball rolls behind. Bright start from both teams.
11 minNow it's Falcao's chance to try his luck as he inherits possession from Di Maria. His effort flies well wide from 25 yards out, but United are rampant right now, with the pace of Di Maria causing plenty of problems.
14 minSome have questioned him (me included), but Rooney is a man in form at Old Trafford:
7 - Wayne Rooney has scored seven goals in his last five Premier League games at Old Trafford. Sweet.
19 minAfter a frantic start from the home side, things have quietened down a touch, with West Ham seeing much more of the ball. Aside from that Valencia chance, they haven't worked the United defence, which will disappoint Allardyce.
22 minCHANCE! Rafael and Rooney have some understanding, that's for sure. Again the little Brazilian gets forward well from full-back and picks out Rooney on the edge of the box. This time his shot is scuffed, though, and easily hacked clear by a retreating Reid.
23 minThat's a second goal for United and West Ham only have themselves to blame. Song loses possession in his own half and United spring forward, with Falcao playing in Van Persie. Having got into the area, the Dutch striker shows a smart stepover to beat Reid, before slotting the ball beyond the reach of Adrian. It's 2-0 United and as it stands, they are comfortable. However, remember, they have blown this type of winning margin recently!
27 minMore fluent football from United as Herrera bursts forward and then plays the ball out wide to Rooney. His cross is as an instant one and aimed for Falcao, but Reid does ever so well to clear the danger for a corner, which comes to nothing. The Colombian's wait for a first Man United goal continues.
31 minFor the first time today, Allardyce has made his way down to the technical area and is barking out some instructions to his players. He's obviously not happy with how his side have started this contest and understandably so.
33 minGoing back to that Van Persie goal for a moment - it was a landmark one for the Dutch international:
35 minCHANCE! What a goal that would have been for United and a player like Di Maria really should be scoring. Van Persie starts it with a clever reverse pass to Herrera, who pulls the ball back from the right byline. Di Maria comes rushing in unmarked, but his shot flies harmlessly wide of the target. You'd expect much, much more from the Argentine.
37 minThis was never over, was it?! The United defence fail to deal with a corner, while De Gea also doesn't cover himself in glory as he comes to claim the ball, but misses it. Reid hits the crossbar with a header from six yards out, but Sakho is standing all alone to nod in from close range. How are the nerves, United fans?
41 minIt's gone very quiet at Old Trafford all of a sudden. You can tell that there are plenty of nerves among the fans flying around the place. Their side are still showing plenty of attacking intent, though. It's a fairly safe bet that there will more goals, probably at both ends!
45 minThere will be two minutes of stoppage time at the end of this first half.
3.51pmAs you expect with United these days, that was an entertaining half of football. They lead 2-1, with both sides providing plenty of signs that there will more goals after the restart.
3.53pmWith the players that United have in an attacking sense, it will be of little surprise for you to hear that they have looked dangerous every time that they go forward. Rooney is arguably having his best game of the campaign, while the likes of Herrera, Di Maria, Falcao and Van Persie have all looked sharp. Defensively, they have also been a bit better, with the West Ham goal being the fault of De Gea. On the whole Van Gaal will be pleased, but he will know this is far from over.
3.56pmMeanwhile, in the other dressing room, Allardyce may be having a few choice words with his players. United are vulnerable - everybody knows that - but for 30 minutes, they barely mounted an attack. The goal seemed to install some belief into the visitors, but you still feel that they have plenty of improvement to make in the final third. Downing, so effective at the tip of a diamond in recent weeks, has barely featured. They need to get him on the ball more regularly.
3.58pmObviously, a lot of the talk before this encounter was concentrated on United's debutant centre-back McNair. To be fair to the youngster, he's looked relatively comfortable so far. He hasn't had too much to do defensively, but what he has had to contend with, he has done so with minimal fuss. There have been occasions where he has been a little wasteful in possession, but he appears confident enough to receive a pass. All in all, he can pleased with his first 45 minutes of Premier League football.
4.01pmLet's get one more statistic from Opta before the second half gets underway. While assists are nice, Falcao must be desperate for a goal of his own:
2 - Falcao has more assists in his last two PL games (2) than he managed in the last three league seasons (1). Craftsman.
46 minRESTART! Hosting United, who lead 2-1, get us back underway at Old Trafford.
49 minBOOKING! It's now one apiece on the bookings front as United midfielder Herrera joins Song in the referee's notebook. The Spaniard went in rather wildly on Poyet and can have few complaints.
52 minSAVE! That was almost the moment for Falcao as his deflected effort appeared to be heading for the top corner of the West Ham net. At the final moment, though, Adrian shows great reflexes to tip away the ball. That's some save from the Spaniard.
55 minSAVE! It's nervy moments for United as Cresswell swings over a cross towards the back post for Sakho, who beats a flat-footed Shaw to the ball. De Gea does really well to push his shot behind for a corner, which also causes problems to the hosts before Herrera is able to boot the ball away from danger. That will have given the away some confidence.
59 minWhat a huge moment this good be with regards to the outcome of this game. Some referees may have brandished a yellow card, but it's stupid from the United skipper as he boots Downing high up on the thigh as he looks to spark a West Ham counter-attack. Downing was in the West Ham half, there was no need for such petulance from Rooney. What will United do now? It looks like Van Persie has dropped deeper, with Falcao now a lone forward.
61 minWEST HAM SUB: The first alteration of the match is made by West Ham, with a quiet Amalfitano being replaced Carlton Cole. That is certainly an attacking switch from Allardyce.
65 minSUBS: More changes, this time from both teams. Van Gaal looks to be attempting to shore things up by taking off Falcao, who does not look best pleased, and bringing on Darren Fletcher. As for the Hammers, Carl Jenkinson has taken the place of Demel at right-back.
68 minWest Ham are certainly in control of proceedings right now. They are having much more of the ball and have United contained inside their own half. Despite that, they haven't really tested De Gea since Rooney was sent off.
72 minBOOKING! United aren't happy because they believe Sakho should be off for his trip on Rafael, who was looking to set his side away on a counter-attack. The difference was that Sakho clipped the heal of his opponents, while Rooney caught a thigh. The yellow card is the right decision.
75 minMAN UNITED SUB: Potentially some more bad news for United on the injury front as Herrera comes off with what looks to be a back problem. He's been replaced by the industrious Antonio Valencia.
77 minWEST HAM SUB: There are subs galore at the moment. Kevin Nolan, who is fit after a stint on the sidelines, replaces Poyet.
80 minStill West Ham are playing a lot of this game in the United half, but chances are proving to be difficult to create. As for the hosts, they are really struggling to keep hold of the ball. The dismissal of Rooney has killed things as far as they are concerned.
84 minGreat defending from McNair as he somehow heads clear a dangerous cross from Jenkinson facing his own goal that it seemed Valencia was going to tap in from close range. West Ham have started to be more direct and United are wobbling somewhat. Their fans, understandably, seem nervous.
88 minJenkinson, brought on as a right-back, has done very well getting forward. He's just won yet another corner for West Ham, but Tomkins nodded it wide at the back post when under pressure. Time is running out for the Hammers.
89 minDISALLOWED GOAL! West Ham thought they were level! It's Jenkinson again with a great low cross, which an unmarked Nolan slides in from close range. He starts to celebrate, but it's cut short by the linesman's flag. Replays show that it was a tight decision that really could have gone either way. West Ham are pushing hard here!
90 minThere will be four minutes of injury time here. A long four minutes as far as United are concerned!
90+1 minBOOKING! Trying to prevent a corner, West Ham goalkeeper Adrian clearly uses his hand outside of the area and is cautioned. As far as United are concerned, the ball is in the right part of the pitch.
90+2 minAnd now the home side have a corner. Time is ticking away.
90+3 minMAN UNITED: It's another United substitute and one designed to waste time you would imagine. Di Maria comes off and is replaced by young defender Tom Thorpe, who is making his United debut.
4.54pmThe referee plays one more minute than the promised four as West Ham pepper the United box with long balls, but the home side hold out well and claim the three points. Old Trafford lets out a huge sigh relief!
4.56pmThat is all we have time for from Old Trafford. Thanks for joining us this afternoon, but be sure to stick with Sports Mole over the next few hours for coverage and reaction from matches at home and abroad, as well as the ongoing Ryder Cup. There really is no reason to go anywhere! Thanks for joining us and until next time goodbye.