Brighton beat Arsenal for the first time since 1982 to increase the pressure on Gunners boss Arsene Wenger.
Lewis Dunk put Brighton ahead when he hooked the ball home from a corner after it dropped to him inside the six-yard box.
The Seagulls added a second when Laurent Koscielny’s misplaced pass was intercepted and Pascal Gross teased a high cross into the box for Glenn Murray to head past Petr Cech.
Arsenal pulled a goal back when Brighton failed to clear their lines. Granit Xhaka fed the ball into Pierre-Emerick Aubameyang, who cleverly flicked the ball home with the outside of his boot.
Arsenal dominated possession in the second half and had a late chance to equalise through Aubameyang but he could only shoot straight at Mathew Ryan.
The Gunners were also fortunate not to have Sead Kolasinac, who had already been booked, sent off for a challenge that ended Ezequiel Schelotto’s involvement.