The result made it three wins in 11 Premier League matches for Mourinho’s Spurs and they are suddenly in danger of being cut adrift from the top four for another campaign, particularly with games against Chelsea, Manchester City and West Ham in three of their next four fixtures.
This abject defeat came against a Brighton side with just one win in 11 games themselves and without a League victory at home all season. Like Liverpool on Thursday night, Spurs could hardly have picked a better time to play the Seagulls but they barely laid a glove on them.
More worrying than the result itself was the performance, as the scoreline actually flattered Spurs. Had it not been for Toby Alderweireld’s brilliant goal-line clearance to deny Aaron Connolly and a succession of other near-misses, Brighton would have won by more.
To illustrate the difference between the two sides, Brighton midfielder Alexis Mac Allister finished the game with seven shots, all fierce efforts from outside the box, while Spurs had eight in total – the majority desperate attempts late in the game as they searched for an undeserved equaliser.
Mourinho’s side had no ideas, no urgency and seemingly no plan, leaving the manager facing big questions about his decisions, not least over his system – which he changed at half-time for the second match running.
Based on this display, Spurs are going backwards under the Portuguese and there are problems for Mourinho to fix all over the pitch.
Without the injured Harry Kane, his attack looked toothless, at least until Carlos Vinicius offered a focal point after the break, while his midfield was overrun and his much-changed defence porous again.
With Chelsea, resurgent under new coach Thomas Tuchel, laying in wait on Thursday, Mourinho must quickly lift his players for what suddenly feels like a potentially seismic game in Spurs’ season.
Defensive errors cost Spurs again
Mourinho responded to the error-strewn defeat to Liverpool by ripping up his back five, but a new-look defence suffered from the same old problems.
Brighton’s goal was all too preventable as Ben Davies got caught the wrong side of Pascal Gross and then Trossard, who finished the German’s cross from inside the box.
By that stage, Spurs had already been given a warning, with Gross striking the post from a similar move in the first few minutes as Brighton totally dominated the first half.
Serge Aurier was bombed out of the squad altogether after storming out of the stadium at half-time on Thursday, with his future now uncertain, while Eric Dier and Matt Doherty also paid the price for mistakes against Liverpool by dropping to the bench.
With both his right-backs out of the picture, Mourinho named Moussa Sissoko at wing-back, where he was ineffectual, while a completely new back three of Alderweireld, Davinson Sanchez and Joe Rodon struggled for cohesion.
The message was clearly that Mourinho will not continue to tolerate individual errors but completely changing the defence was a bad way to build confidence and unity, while persisting with wing-backs without either right-back or Sergio Reguilon left too many square pegs.
Mourinho unsurprising switched to a back four at half-time, just as he did against Liverpool, but Spurs remained wide open at the back and had Alderweireld to thank that Brighton did not double their lead through Connolly.
Spurs toothless without Kane
Spurs began an undetermined period without Harry Kane at the Amex, with Heung-min Son, Steven Bergwijn and Gareth Bale deputising up front for the injured England captain.
Mourinho is on record saying neither Son, Bergwijn nor Bale is a striker and sure enough Spurs were toothless and totally lacking a focal point in the first half.
The introduction of Vincius at the interval at least offered Spurs a target man and the Brazilian went closest to a leveller, forcing Robert Sanchez into a full stretch save.
It begged the question of why Vinicius did not start the game, although he is likely to be given a chance against Chelsea.
Bale’s performance on just his second Premier League start since returning was again concerning, with the Welshman looking off the pace and proving ineffective before he was hooked for Lucas Moura on the hour.
Mourinho’s side finished with five forwards on the pitch and practically no midfield but it made little difference, with Brighton looking the more likely to score again.