The set-back, which came on the back of five wins in a row in all competitions and denied Spurs a chance to move into the top six, was almost unthinkable at half-time when the north London side had dominated play and taken what looked like a decisive lead through Brennan Johnson and James Maddison.

But the way they collapsed after the break to be steamrolled by Brighton, who scored through Yankuba Minteh, Georginio Rutter and Danny Welbeck to take three points, left Postecoglou bewildered and hurt.

He cut a morose figure in the post-match press conference and, perhaps for the first time since taking over as manager in June 2023, was not afraid to criticise his players for their total collapse on the south coast.

“We weren’t competitive, we didn’t win our duels, we lacked intensity. We didn’t deliver the things you need to do at this level, the basics of the game, and we paid the cost,” he said.

“Straight after the game you are emotional, but I’d say that’s probably my most disappointing loss since I’ve been here in terms of the way we went about it and it’s something I need to assess.

“It was a stark reminder of what elite sport is about. The core of it is to be competitive. If you’re not competitive it doesn’t matter how good you are – or how good you think you are – you are going to trip up.”

The insinuation there, perhaps, is that Tottenham’s players became complacent after five wins in a row and a strong first half performance at the Amex in which they dominated the game and looked irrepressible in attack.

But there was little chance of Postecoglou defending his players after watching their limp second half performance in which poor defending, particularly from Destiny Udogie, gifted Brighton three goals – before Spurs virtually gave up with almost half an hour to go.

Postecoglou said: “I don’t know if it was complacency, I don’t know where it comes from and that doesn’t really matter to me. Wherever it comes from it’s unacceptable at the end of the day.

“You’ve got to understand you’re not going to win every game. But it’s the first time we’ve lost game in that manner since I’ve been here and it’s unacceptable “If you don’t compete and you allow the opponent to overrun you in that manner you’re not going to win.

“I’m sure the players are disappointed, but I don’t really care about that. They should be disappointed. I want them to understand that disappointment comes from us not doing the very basics of what is expected.” It’s unusual to hear Postecoglou speak in that way, and you certainly wouldn’t want to be a Tottenham player when the match is analysed in back in north London.

The Australian will have some serious questions to ask about the nature of his side’s collapse, just when it seemed evidence of their top-four credentials was building.

Their first-half dominance was so complete, and the performance so impressive, that if you watched that opening 45 minutes in isolation you would almost certainly conclude that Spurs are good enough to challenge the big boys.

But by the 66th minute, when they were 3-2 down, the lack of mental and physical energy in the side – and the lack of belief – hinted that all those deeper problems that have dogged the club for decades are still easily prodded.

Opta stats encouraged a ‘Tottenham have gone all Spursy’ headline by confirming they have now lost a Premier League game after being two or more goals ahead 10 times – the first club to hit double figures with that unfortunate stat.

Postecoglou knows that, of course, but what is frustrating for Spurs fans is that just when you thought the Australian coach had built a thicker skin for his team, the ease at which it was peeled off by Brighton.

They scored just minutes into the second half when Kaoru Mitoma crossed low, Udogie completely failed to deal with it and Minteh pounded.

It was 2-2 when Mitoma set up Rutter to score smartly and then 3-2 when Udogie fell asleep in the box, allowing Rutter to reach a ball he should never have got near – and cross for Welbeck to head home.

There was still 30 minutes left but Spurs were bereft of confidence or ideas – and Brighton saw it out comfortably.

Albion manager Fabian Hurzeler said: “I have a lot of trust and belief in the potential of the team. At half time we spoke about fulfilling our plan with more energy and being more intense.

“We weren’t ready for the intensity of Tottenham in the first half. I’m proud of how the team reacted. We showed character, took responsibility and then created chances in the second half.” Pride was not a word that Postecoglou used, despite his team’s impressive first half display. All he could remember was the misery of their collapse, and another painful example of what has been a Tottenham trait for far too long.

“It’s a terrible loss, as bad as it gets,” he concluded.

Brighton: Verbruggen 6; Veltman 5, Webster 5 (Igor 9), Dunk 7, Kadioglu 5 (Estupinan 46; 7); Baleba 6 (Wieffer, 74; 6), Hinshelwood 6; Minteh 7, Mitoma 8, Rutter 7 (Enciso, 73; 6); Welbeck 7.

Unused subs: Steele, Lamptey, Ayari, Gruda, Ferguson.

Tottenham: Vicario 6; Udogie 5, Van de Ven 6, Romero 5, Porro 6; Kulusevski 7, Bentancur 6 (Bissouma 79; 6), Maddison 8 (Moore 85; 6); Johnson 7, Solanke 7, Werner 6 (Sarr 79; 6) Subs: Forster, Dragusin, Gray, Spence, Sarr, Bergvall, Lankshear.

Referee: David Coote