Declan Rice marked his return to West Ham, but it was Arsenal who dominated with a resounding 6-0 victory in a decisive statement for their Premier League title aspirations.
Bukayo Saka scored twice, while Leandro Trossard, William Saliba, and Gabriel Magalhaes also found the net in a commanding performance by Mikel Arteta's side.
The win, setting a new club record for Arsenal's biggest Premier League away victory, places them just two points behind leaders Liverpool and trailing Manchester City only on goal difference.
After a shaky period with one win in seven games around the new year, Arsenal bounced back strongly following a two-week winter break.
West Ham, who had defeated Arsenal twice earlier in the season, found themselves outclassed in a match that increased scrutiny on manager David Moyes, whose contract expires at the season's end.
Saliba opened the scoring from Rice's corner, signaling an onslaught that continued with Saka converting a penalty and Gabriel heading in another Rice delivery.
The pain for West Ham intensified when Trossard skillfully fired into the top corner just before halftime. As the second half played out in front of numerous empty seats, Saka netted his 50th Arsenal goal with a trademark left-footed strike, followed by Rice's stunning long-range finish.
The former West Ham captain refrained from celebrating out of respect for his former club. The convincing victory provides further momentum for Arsenal in the title race, building on their recent 3-1 win over Liverpool.