Manuel Lanzini’s goal in the ninth minute earned David Moyes his first victory over his former employer since leaving the club in 2014.
Moyes made 10 changes on his side to keep things cool after the weekend and the visitors are off to a good start.
Jarrod Bowen shot wide in five minutes before debutant Alex Kral saw an effort blocked by Eric Bailly.
The Hammers kept the pressure on and were rewarded before the clock hit 10 minutes thanks to some wonderful play from Ryan Fredericks. The full-back, who impressed in the Europa League last week, slipped between the static pair of Alex Telles and Jadon Sancho to reach the signing and cut back for Lanzini, who kicked the ball into the corner most distant.
Manchester United fought back with a flurry of chances, including Juan Mata hitting the bar from a tight angle, but the visitors managed to pause with Alphonse Areola’s clean sheet intact on his first start for the club.
The hosts are still struggling to really test the French keeper after the break, although the former Fulham man did well with what was sent to him.
Ole Gunnar Solskjaer sent Mason Greenwood and Bruno Fernandes to try and find a leveler, but West Ham held on.
Andriy Yarmolenko and Mark Noble both missed out on a superb chance to win the game in the final five minutes, the former hitting the post after rounding Dean Henderson before the latter directly hit the United goalkeeper.
Luckily for the visitors, this time Manchester United didn’t charge them late.
Here’s how Jack Rosser rated the Hammers …
Fantastic debut for the Frenchman, one that will certainly make Lukasz Fabianski nervous. Commander in the back and made some nice saves.
A brief but brilliant appearance for the rear side. Wonderful race between two United players before giving Lanzini the start for the first goal.
A solid comeback for Dawson after a difficult start to the season. No-frills display.
Nice performance from the center-half, who wanted to take his chance to impress. Did a strong Lingard block at the break.
A good performance for his first start of the season. Strong and hardworking from the back but not afraid to push forward. The end product needs work.
Hairy moments from the West Ham captain, who sometimes watched the pace but handled the game well. A good response to the missed penalty on Sunday.
A very confident start for the last Czech companion at West Ham. Not out of rhythm or fearful in his debut in English football. Positive on the ball too.
Running tireless as usual ahead and was a threat at the break. The finish is still lacking, however.
Clean and tidy on the ball in midfield and pulled off a nice finish to make the most of West Ham’s strong start. His first goal since that strike against Tottenham.
Solid performance on his return to the starting XI after an injury. Assisted Johnson defensively and his pace was useful going forward.
Put a real shift on the right side and reach promising positions. Good move from the start to set up Bowen. I should have done it two late.
Professional performance from the rear side after being called in much earlier than expected.
Never really entered the game after its introduction.
Reinforced the left side and offered more out of possession than Lanzini.