Ricardo Vaz Te scored his first goal for the Hammers since the play-off final last year when Andy Carroll nodded a Matt Jarvis cross into his path after only 16 minutes.
The Hammers continued to dominate the game for the first half an hour and it wasn’t until Reds midfielder Kagawa broke through the defence to slide the ball to Antonio Valencia to tap in, that they showed any of their class.
The Hammers started the better in the second-half and again took the lead on 55 minutes when Mo Diame curled a beautiful strike passed David De Gea.
As expected, Man Utd started to come back at the Hammers but they looked to be holding on resolutely until Robin Van Persie struck a rebound high into the net when he looked to be in an offside position.
Unfortunately for the Hammers the linesmen raise his flag and the goal was allowed to stand.