Arsenal's fading title hopes were dealt a devastating blow after losing to Brighton to leave leaders Manchester City one win from a fifth Premier League title in six seasons.
The Gunners needed to respond after City's 3-0 win over Everton earlier on Sunday left Mikel Arteta's side trailing by four points in the race for the title.
On a deeply frustrating day for Arsenal, Leandro Trossard hit the bar against his former club while Martin Odegaard and Bukayo Saka both went close before Julio Enciso's close-range header put Brighton ahead.
Substitute Deniz Undav doubled the lead after lobbing Aaron Ramsdale in the 86th minute before Pervis Estupinan added to Arsenal's misery with Brighton's third in the 96th minute.