Brighton produced a stunning second-half comeback as they scored three goals in 18 minutes to come from 2-0 down to beat Tottenham 3-2 at the Amex Stadium.
Spurs were in total control at half-time thanks to goals from Brennan Johnson, who scored for a sixth straight game, and James Maddison.
But Ange Postecoglou's side suffered a shocking collapse sparked by Yankuba Minteh's goal just three minutes into the second half as he pounced on Destiny Udogie's mistake.
As it happened: How Spurs collapsed on the south coast
Teams | Match stats: Brighton make stunning second-half turnaround
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Rocked by the goal, Brighton sensed Spurs' loss of confidence and found a leveller 10 minutes later through Georginio Rutter's low finish.
The comeback was then complete in the 66th minute as more poor Spurs defending allowed Danny Welbeck to head home.
The shocked visitors failed to recover from going behind, mustering just one shot on target as Tottenham suffered their first defeat in six games to leave the north London side ninth and four points off the top four heading into the October international break.
Brighton, meanwhile, end their four-game winless run to move sixth and two points behind fourth-placed Chelsea.
Ange: Worst defeat of my Spurs tenure
Spurs boss Ange Postecoglou speaking to Sky Sports:
"It's disappointing. I'm absolutely gutted with that. It's probably the worst defeat we've had since I've been here.
"It's unacceptable in the second half, we weren't anywhere near where we should be. Maybe we got carried away with how we were going.
"We kind of accepted our fate and we haven't done that since I've been here - usually we fight for everything, but when you don't you pay the price and we paid the price.
"Maybe things were travelling on too smoothly and football and life will trip you up if you get too far ahead of yourselves and that's what it looked like in the second half.
"It's a terrible loss for us. As bad as it gets. There is one way to fix it and that's my responsibility.
"We lost all our duels, we weren't competitive. Irrespective of what you do tactically, we weren't competitive.
"The majority of players are going on international duty so they will process it individually. And I'll deal with it when everyone gets back."
Maddison: We lost complete control after Brighton's first goal
Tottenham midfielder James Maddison speaking to Sky Sports:
"We couldn't deal with the mental shift and lost complete control of the game after the first goal went in. We dealt with the momentum very poorly. It just felt like attack after attack and we couldn't deal with it.
"Brighton are a good side but when the first goal went in you have to deal with adversity in the Premier League and stay strong, weather the storm. The best teams stay strong. We didn't do that.
"We'll need to take big lessons from the second half if we want to make strides forward."
Hurzeler on what he said at half-time
Brighton head coach Fabian Hurzeler speaking to Sky Sports:
"The first half was not a tactical thing where we conceded the two goals, it was about making the last step, playing with intensity, fulfilling the match plan with intensity. We tried to get this back in half-time, but it's the job of the players. They played an amazing second half and showed the reaction and deserved to win.
"A little bit was missing, a little bit of intensity, being ruthless in the most important duels. If you win the personal duels, if you gain the ball in the opponent's half, you gain self-confidence. That was the biggest change in the second half, that we won more balls.
"Tottenham had some moments in our half, but most of the times we controlled the transitions. Then I always say we have enough quality in possession to always score. For me it's very important that we learned from the first half. Not everything was bad, even though it seemed to be bad being 2-0 down, but there were positive things."
Analysis: Solanke shines but Spurs fail to capitalise
Sky Sports' Lewis Jones:
Ange Postecoglou blamed Tottenham's incredible collapse at Brighton on a lack of application rather than anything that tactically changed in the second half. That is hard to argue against yet, what was glaring obvious after the break was how little of the ball Spurs managed to get into Dominic Solanke. The striker was excellent for 45 minutes, playing a huge role in both goals and offering Spurs an option to set their attacks from.
Despite his influence, Solanke only had 20 touches of the ball in the entire game, the fewest of any player that started the game across both teams. Spurs should've utilised him more, especially in the second half where he was anonymous as Tottenham failed miserably at chasing the game when 3-2 behind.
Former Spurs striker Les Ferdinand was left perplexed about the lack of service Solanke got, he said: "In the first half Spurs always had the out-ball with Solanke - they never used him in the second half. He never got the chance to hold it up and bring people in. He hardly touched the ball, through no fault of his own."
Brighton's key player, Kaoru Mitoma, had 51 touches. Play to your strengths they say. That proved the difference between the teams.
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