Mikel Arteta’s men were looking to pick up where they left off before the World Cup break, but were dealt a blow on the counter despite a rapid start.
Jarrod Bowen won a penalty thanks to a reckless challenge by William Saliba, which was powerfully converted from 12 yards by Saïd Benrahma to earn a surprising lead.
Staying true to their patient style of play, Mikel Arteta’s troops gradually made headway, but time and again failed to find a decisive opening that would put the Hammers at risk of yet another winless match on the road.
The breakthrough looked to have arrived on the brink of HT after Aaron Cresswell was penalised for handball inside the area, but VAR intervened to send the visitors into HT with their lead intact.
The Gunners raised the stakes immediately after the restart, putting their London neighbours to the sword with two quickfire goals to change the complexion of the match.
Bukayo Saka made up for his earlier disallowed goal by striking his effort into the bottom left corner after carelessly being played onside by Vladimir Coufal, minutes before Gabriel Martinelli squeezed an unstoppable low drive past Fabiański to complete the turnaround.
West Ham’s morale was visibly affected, as they faltered further and conceded a third as Eddie Nketiah superbly turned Thilo Kehrer before finishing into the bottom left corner.
That would be the final nail in the Hammers' coffin, as Arsenal shut David Moyes' side out of the game.
The festive season has been nothing but merry for West Ham, who've won just one of their last nine PL games on Boxing Day.
The visitors are now just one point clear of the relegation zone, and could drop into the bottom three if results elsewhere go against them.
Flashscore Man of the Match: Martin Ødegaard (Arsenal)
