Arsenal missed the chance to close the gap on Premier League leaders Liverpool as West Ham ended a four-match winless run with a stunning victory at Emirates Stadium.
Jarrod Bowen got the winner against a Gunners side who later had Myles Lewis-Skelly sent off.
Victory would have moved Arsenal to within five points of Arne Slot’s team, who visit champions Manchester City on Sunday, but they struggled badly against a Hammers side who defended magnificently and created the better openings over the 90 minutes.
Bowen started and finished the move that led to the winner late in the first half, collecting a loose ball on the edge of his own box and feeding Aaron Wan-Bissaka before stooping low to nod the full-back’s cross into the net for his 50th Premier League goal.
It was the first time Arsenal had trailed in a home Premier league game at half-time this season, but they showed no discernible improvement after the interval – despite pinning West Ham back for much of the second period.
Leandro Trossard had a low shot saved by the feet of Alphonse Areola, but the Gunners’ hopes of a route back into the contest were dealt a major blow when Lewis-Skelly was sent off for a professional foul on Mohammed Kudus near the halfway line.
Referee Craig Pawson initially cautioned the 18-year-old for dragging Kudus to the floor, but the video assistant referee (VAR) ruled that Lewis-Skelly had denied the Ghanaian a clear goalscoring opportunity and the yellow card was upgraded to a red.
West Ham held on comfortably in the end to move 13 points clear of the bottom three and level with Manchester United in 15th – although they stay 16th because of their inferior goal difference.