Goals from Andriy Yarmolenko and Aaron Cresswell ensured West Ham recorded a convincing 2-0 victory over an injury-hit Manchester United to move fifth in the Premier League.
The Hammers went after the visitors from the off and were rewarded with a deserved lead as Yarmolenko struck a half-volley past a diving David de Gea on the stroke of half-time after some fine one-touch football.
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While United started the second half brightly, an injury to Marcus Rashford stunted hopes of a comeback that were put fully to rest when Cresswell scored a wonderful free-kick five minutes from time.
Ole Gunnar Solskjaer's side went home with nothing except a longer injury list, while Manuel Pellegrini's men celebrated their third win of the season.
West Ham add insult to injury
United's depleted frontline struggled to deal with a physical West Ham defence that nullified the marauding runs of Daniel James and Rashford, harrying the forwards into corners, giving them little time or space.
While the visitors rushed their attacks and gave possession away freely, West Ham's attacking triumvirate were patient in the final third, looking for gaps in their opponent's backline and using the excellent Mark Noble as an anchor in midfield when they needed to go backwards.
Their best piece of football was rewarded when Noble found Felipe Anderson on the edge of the box, the Brazilian playing a wonderful first-time ball into Yarmolenko as he ran into the box, the Ukrainian taking one touch for control before rifling past De Gea.
The visitors made a much better start to the second half and should have gone level when Juan Mata missed a glorious opportunity with the goal gaping, only to divert Andreas Pereira's excellent cross a yard wide and into the stands.
But United were dealt another huge blow when Rashford pulled up injured in the box and was immediately replaced by Jesse Lingard, leaving a tired side without a recognised striker on the pitch.
Five minutes from time, left-back Cresswell put Solskjaer's men out of their misery with a wonderful free-kick from 25 yards, bending the ball beyond the reach of De Gea for a West Ham win and all three points.
What the managers said
Manuel Pellegrini: "We had the personality to play against United at home. It's a big thing, trying to win the game from the first minute. We had to be a very solid and consistent team.
We pressed, we recovered, we didn't allow them to play in space. We need to work in defending, but our intention was to recover the ball.
In the first 45 minutes, we lost the ball too much, so to score the first goal was a key factor in winning the game.
Ole Gunnar Solskjaer: "It's a disappointing day overall. With this group, I know the character of the boys, of course they are disappointed, they are very down at the moment. Knowing them, they will be back. We have a big game against Arsenal in the league and Rochdale in midweek."
"The big key moments in the game went for West Ham and against us. The two finishes they've had are great, two great goals. We also created chances we should have taken. We didn't really grasp the moments that we should have. We'll improve."
The pundit verdict: 'No United positives'
Roy Keane: "I was shocked and saddened by how bad they were."
Jose Mourinho: "I can't find any positives. We were bad last season, but I don't see any improvement this season."
Gary Neville: "I've said over the last few weeks, watching this team and squad that it's not ready. There are going to be ups and downs and lots of pain. It was painful today but it doesn't make it any easier when you see it with your own eyes. In that first half they were lethargic. I thought it was the most disappointing first 45 of the season."
Man of the match: Mark Noble
Noble ran the show for West Ham - exactly the kind of player United were missing in the midfield. He made Matic look average and was vital in setting up the opener. He also won the free-kick that sealed the win.
"There's a real feelgood factor. It gives us belief," he told Sky Sports after the game.
What's next?
West Ham face a trip to the south coast to face Bournemouth, while Manchester United face Arsenal next Monday, live on Monday Night Football.