Marcus Rashford’s only goal was enough to send Manchester United to the fourth position on the league table after 22 games.
The England forward converted home a low cross from Edison Cavani in the 93rd minute to give West Ham their second straight defeat recently.
Jarrod Bowen and Declan Rice had both gone close for the Irons earlier on in the second half in a match which ebbed and flowed, but looked in all likelihood destined for a draw until Rashford’s cruel late intervention.
West Ham’s side are currently a point and a place behind Manchester United in the Premier League table.