Neal Maupay scored with seconds left to gift Brighton a crucial win in the relegation battle and sink Arsenal to a second defeat in as many games since the Premier League’s restart.
After a sluggish start in which Alexandre Lacazette’s header was the only decent chance, the game exploded into life in the second half.
Pierre-Emerick Aubameyang had three notable chances to score his 50th Premier League goal, with the best chance being ruled out for offside.
For all of the Gabon international’s involvement, however, it was Pepe who broke the deadlock three minutes later, curling the ball from the right side of the box into the top left corner.
But Brighton responded minutes later and Lewis Dunk was quickest to react to a goalmouth scramble and poke the ball home from a couple of yards away.
The Seagulls were not done there, however, and Maupay popped up after a brilliant passing exchange to slot home and stun the hosts.
Tensions boiled over afterwards, too, when Maupay appeared to brush past Matteo Guendouzi.
The game was somewhat overshadowed, however, by the serious knee injury suffered by Gunners goalkeeper Bernd Leno, who was stretchered off suffered after slipping awkwardly in his attempts to collect the ball.