A late Joao Pedro header stunned Manchester United, sending the Amex Stadium wild after a 2-1 win for Brighton and Hove Albion.
The win sends Fabian Hurzeler's side to the top of the Premier League table having also defeated Everton 3-0 last weekend.
Former Manchester United player Danny Welbeck haunted his old club, giving the home side an early lead after a probing cross from Japanese winger Kaoru Mitoma in the 32nd minute.
Erik ten Hag's side improved in the second half with winger Amad Diallo levelling the game up in the 60th minute with a fine individual effort.
Substitute Alejandro Garnacho thought he'd given Manchester United the lead shortly afterwards, but his goal was ruled out after an unfortunate touch from the offside Joshua Zirkzee.
Manchester United continued to press for a winner but Brighton turned the tables with Brazilian forward Pedro nodding Adingra's cross home deep into stoppage time.
On commentary, Ally McCoist was critical of United's left back Diogo Dalot for his role in the goal.
"Completely and utterly unmarked.
"McTominay and De Ligt look at each other to say, 'where's my left back? I don't know what's going on on the left hand side of the defence."
Dalot was closer to the right hand side of defence, leaving space for Brighton to capitalise in the penalty area.
Rio Ferdinand criticised United's defence for their 'grave lack of concentration,' and also called out Antony's 'powder-puff' tackle in the build-up.
On the whole, the former centre half felt United's performance was positive, however.
"I think a draw would have been a fair result," he said on TNT Sport.
"The turning point was that disallowed. After that, a grave lack of concentration cost Manchester United. You get punished.
"There was a huge space at the back post and you can't have that at this level.
"Someone's got to be shouting, to take control of that situation. And unfortunately today, nobody did."
"It's a powder-puff tackle (from Antony.)
"He has to smash that and go through it.
"On the whole, I think the performance was a lot more positive than last season.
One moment could have changed this game, but this isn't an if-buts-and-maybes game," he added.
