Managerless Arsenal's season plummeted to a new low as they were beaten by Brighton in interim manager Freddie Ljungberg's first home match in charge.
Alexandre Lacazette marked his 100th Gunners appearance by heading his side level after Adam Webster had given the visitors a first-half lead.
With the score 1-1, there was frustration for Ljungberg and Arsenal when David Luiz thought he had made it 2-1 with a volley but it was correctly ruled out following a VAR check for offside.
Neal Maupay headed Brighton's winner from Aaron Mooy's cross to leave Arsenal on their worst winless run since 1977 - and 10 points off a Champions League spot.