Arsenal came from behind to end their nine-match winless streak as Freddie Ljungberg enjoyed his first victory as interim manager at the expense of his former club West Ham.
Eighteen-year-old Gabriel Martinelli marked his full Premier League debut by side-footing an equaliser which cancelled out Angelo Ogbonna’s deflected first-half opener at London Stadium.
Within nine minutes, Nicolas Pepe had curled a magnificent second into the top corner and Pierre-Emerick Aubameyang fired in a third.
The salvo turned the game on its head and piled the pressure on West Ham boss Manuel Pellegrini, whose side have taken four points from their past nine league games and conceded three times in three successive home games.
The Hammers remain a point above the relegation zone in 16th and face a trip to third-bottom Southampton on Saturday. Arsenal move up two places to ninth.
What now for the unhappy Hammers?
When they beat Chelsea nine days ago to end their own winless sequence, it appeared West Ham were on an upward curve.
The combination of boos and thousands of empty seats that accompanied the final whistle on Monday underlined the truth of the matter.
West Ham are perilously close to dropping into the relegation zone, something the club cannot countenance after moving to the 60,000-capacity London Stadium.
Even if Pellegrini survives this defeat, if West Ham lose again at Southampton on Saturday the calls for his dismissal will become piercingly loud. This was the third home game running in which they had conceded three goals.
The Hammers were not particularly convincing when they were in front. Once they lost the advantage, the lack of confidence so clear in Arsenal’s play transferred to theirs.
Record signing Sebastien Haller was left on the bench and even when he was introduced 20 minutes from time, he made no noticeable impact.