Emi Buendia scored with the last kick of the game as Aston Villa stunned Arsenal to move three points behind the Premier League leaders.
Leandro Trossard’s sixth goal of the season looked to have earned a point for Arsenal after he cancelled out Matty Cash’s opener.
But Buendia struck in the 95th minute as Unai Emery’s side moved into second in the table.
Arsenal, who blew Bayern Munich and Tottenham away last month, suffered their first defeat in the league since losing 1-0 at Liverpool in August.
Villa Park erupted after substitute Buendia scored to give Villa their seventh straight game in all competitions.
Eberechi Eze had a goal disallowed for offside before the hosts took a first-half lead when Arsenal – especially Eze – switched off to allow Cash to drill in at the far post.
Arsenal emerged re-energised after the break when Mikel Arteta introduced Viktor Gyokeres and Trossard, who levelled with his 50th Premier League goal, having already gone close.
Emi Martinez brilliantly tipped Martin Odegaard’s shot over as Arsenal looked for a winner, but Buendia stole the points in dramatic style, curling in after Arsenal failed to clear.
