Jarrod Bowen scored an injury-time penalty to condemn Manchester United to a 2-1 defeat in the Premier League and ease pressure on manager Julen Lopetegui.
Casemiro thought he grabbed a point for the visitors when he headed home with less than 10 minutes left to cancel out Crysencio Summerville’s 74th-minute opener.
But United were furious as referee David Coote was sent to the pitchside monitor by the Video Assistant Referee with three minutes remaining to review Matthijs de Ligt’s challenge on Danny Ings in the box.
Despite protests from United’s players over a handball by Ings, Coote pointed to the spot and Bowen calmly converted, slotting past Andre Onana.
United dominated possession and chances in the first half at London Stadium, but the visitors lacked a clinical edge and were left to rue their missed chances.
After a lacklustre first half, West Ham were an improved side after the interval and peppered United’s box with attacks, and they were eventually rewarded when Summerville slid in to direct Ings’ scuffed effort into the back of the net.
The result leaves United 14th in the Premier League with just three wins in their opening nine matches, piling further pressure on manager Erik ten Hag.
It is a statement win for West Ham, however, as they move one place above United after an underwhelming start to the season.