Neal Maupay scored the winner five minutes into added time as relegation-threatened Brighton clinched a huge win over Arsenal, who once again lost a key player to injury.
The French striker showed coolness and class to slot in his ninth and most important goal of the season, win the game for Albion and cap a remarkable comeback.
Nicolas Pepe had fired the Gunners into a deserved lead with a superb curling shot with just over 20 minutes to go, but Lewis Dunk scrambled an equaliser over the line from close range to set up a barnstorming finish.
Maupay's winner was a sucker punch to the Gunners, who have now lost back-to-back games since the Premier League returned - results that surely make a late run to Champions League qualification very unlikely.
They may also have to navigate the rest of the season without goalkeeper Bernd Leno, who was stretchered off after landing awkwardly on his ankle in the first half.
He joins defender Pablo Mari and midfielder Granit Xhaka on the sidelines, both of whom were injured in Wednesday's 3-0 loss at Manchester City.
There is no such negativity for Brighton, though. They appeared to come through the game largely unscathed but are now five points above the bottom three.