United started the game very poorly and went behind when Diafra Sakho scored within 10 minutes. The Hammers dominated throughout the first half but failed to get the crucial second goal their play deserved.
The Red Devils came out in the second half much better and thanks to a brace of goals from Anthony Martial, went 2-1 up in the 73rd minute. The problem though from there was that the lead didn't last long as Michail Antonio headed in a great cross from Dimitri Payet to make it 2-2.
Four minutes later West Ham got their winner and again it came from a cross from Payet, which found the head of defender Winston Reid who powered a header past the helpless David de Gea.
The cost of defeat now means that the Reds need a favour from Swansea City on Sunday when they play Manchester City. United play at home to Bournemouth at the same time hoping to take advantage if City do slip up.
The problem though is that it shouldn't have gotten to this point as the Red Devils had it in their hands before the game but they failed to capitalise. So after the defeat what was learnt from the game?
Martial can't do it all on his own
Martial made it 17 goals in his debut season for United so far with two more on Tuesday, which is a fantastic outlay from the striker.
The French forward showed his class in the second half of the game, taking on the West Ham defence at will and it looked like he was going to give the team a vital win.
The problem though is that Martial can't do it all on his own and needs help from his teammates. The defending after United had taken the lead was shambolic and they let Martial down after he almost single-handedly got United across the line in such a crucial match.
So many players struggling with confidence in the team
One problem during the game that was evident to see was that a few players in the team are struggling with confidence. Morgan Schneiderlin and Ander Herrera were just two of the players that were unable to produce their best during the game, which proved costly.
Schneiderlin was brought off at half-time after struggling to get to grips with the game in the first-half, which was disappointing to see. Herrera also was at fault during the game for a lot of misplaced passes which he needs to work on.
Overall things need to change to give the players more of a chance to show what they can do, instead of them being taken off when they make one mistake.
Blind is not a centre-back
West Ham had a tactic during the game to expose Daley Blind at the back with the height of Andy Carroll. This tactic worked too, as Blind struggled throughout the game and looked like someone who needs a long rest.
Blind has had a very good season for United, but Tuesday showed why he should be used in midfield and not as a centre-back.
It's a pity for him because he has been a vital part of the United defence this season and one terrible game highlights why things need to change in the summer, with a new centre-back being bought.
Rojo deserves to be dropped
Marcos Rojo once again produced a very lacklustre display at left-back which was costly in a game of such magnitude.
Rojo has struggled since coming back from injury and needs to be dropped for his own good. The defender started well at the club but has gone downhill this season and, until things change, it is hard to see how he has a future at the club.