Tottenham were stunned by Sporting Lisbon as two late goals condemned Antonio Conte's side to a 2-0 defeat in their Champions League Group D clash at Estadio Jose Alvalade.
The game appeared to be heading for a stalemate before Sporting substitute Paulinho headed a Pedro Goncalves corner past Hugo Lloris in the final minute of normal time.
The hosts then wrapped up the points in stoppage time when Arthur Gomes, another substitute, cut in from the left and breezed past Cristian Romero and Emerson Royal before slotting a low finish into the corner.
Spurs, back in action after the weekend's Premier League postponements following the death of Queen Elizabeth II, were a long way below their best on the night, struggling to create clear chances and unable to contain Sporting's counter-attacking threat.
It seemed they would at least take a point back to north London, but in the end their lacklustre performance was punished as Sporting celebrated a win which keeps them top of Group D, leaving Conte to concede that his side could have done "much better".
How Sporting shocked Spurs
After a period of silence in tribute to The Queen before kick-off, Sporting were soon showing their counter-attacking potency, pouncing on Spurs errors repeatedly, with Pedro Goncalves forcing a low save from a full-stretch Lloris in the early stages.
That opportunity was created by Marcus Edwards and the former Tottenham youngster continued to cause problems for his old side, most notably when he embarked on a mesmerising dribble shortly before the break, dancing through a crowd of Spurs players and exchanging passes with Trincao before releasing a toe-poked shot which squirmed past the post off Lloris.
Spurs, by contrast, were sloppy and sluggish in possession, their first-half performance summed up by the sight of Richarlison, their two-goal hero against Marseille last week, being repeatedly caught offside.
The visitors did rally after the break, creating a flurry of chances, with Royal heading wide then firing a low shot straight at Sporting goalkeeper Antonio Adan in the space of a couple of minutes.
Harry Kane then drew another save from Adan, while Richarlison fired wide on one occasion, then sent a header past the post on another, but Sporting soon regained their composure.
Having nullified Spurs' attacking threat, the breakthrough arrived from a set-piece as, moments after Lloris had pulled off a brilliant save from Pedro Porro, Paulinho rose highest to head home the subsequent corner at the near post.
Things then went from bad to worse for Spurs when Gomes' superb second goal sparked more wild celebrations at Estadio Jose Alvalade, leaving Conte with much to ponder ahead of Tottenham's Premier League meeting with Leicester, live on Sky Sports on Saturday.
Conte: We can do much better
Tottenham head coach Antonio Conte to BT Sport:
"Difficult result. For sure when you lose the game you are not happy. Today the game was in balance in the second half.
"We could score and we tried to win the game. In the last 10 minutes, we can do much better.
"They score with a corner and then we concede the second goal. A difficult game for sure. We tried to get the win but then at the end we lost the game.
"When you arrive you have to try to fill the box. You have to be accurate and be stronger to attack the goal. We can do much better.
"Now we have to try to rest and to think the next game in the Premier League."
Edwards: Great feeling to beat Spurs
Sporting Lisbon's Marcus Edwards to BT Sport:
"It feels great. I think we deserved it. We showed how we can play. I wouldn't say extra special, but it was a special feeling to play against Spurs. It was good to see people I know - players and coaching staff.
"I stayed the same. Focus was the same. It's a proper family environment here and I couldn't be happier.
"It's home, so of course I want to come back there [to the Premier League] one day. I just focus on what I'm doing here for now."
Analysis: Edwards shows Spurs erred in selling him
Sky Sports' Nick Wright:
Marcus Edwards insisted there was no added motivation in facing his former club when interviewed immediately afterwards but it did not look that way out on the pitch. Edwards played like a young man with a point to prove.
The 23-year-old, born and raised in Enfield and a Spurs player from the age of eight until he was 20, was the outstanding performer as Sporting Lisbon stunned Antonio Conte's side at Estadio Jose Alvalade.
Spurs could not live with him in the first half, his speed on the break making him a dangerous outlet from as early as the seventh minute, when he motored forward and teed up Pedro Goncalves for a low shot which required a sprawling save from Hugo Lloris.
There were plenty more eye-catching moments to follow but the best of them came shortly before half-time when Edwards, once likened to Lionel Messi by Mauricio Pochettino, embarked on a magical run the man himself would have been proud of.
Edwards completed five dribbles in the first half alone - two more than anyone else managed in the entire game - and there was intelligence to his play too, evident in the positions he took up between the lines as Sporting's false nine.
His performance was a continuation of a fine start to the season in Portugal and it will leave some at Spurs red-faced.
His boyhood club had high hopes for him in his youth but a player long regarded as the most talented of his generation at Spurs was sold in 2019 having only been afforded one senior appearance. How they must regret that now. Edwards looks destined for big things.
Analysis: What's happened to Son?
Sky Sports' Laura Hunter:
Heung-Min Son's goal drought continues. The last time the forward hit the back of the net was for South Korea back in June. You have to journey all the way back to mid-May for Son's last entry in a Spurs shirt. Eight appearances, zero goals this season.
By his very high standards, something is off. It is not just a lack of goal involvements that will be concerning for Antonio Conte - his industry and endeavour also appear to have taken a knock.
He cut a forlorn figure when coming off the pitch in the 72nd minute to make way for Dejan Kulusevski. The wonderfully-cheery Son smile, for which he is famed, has disappeared. Sombre Son is the new guise.
Conte spoke in the game's preamble about the importance of utilising his squad in Champions League competition but only made one change - while Sporting's introductions dramatically altered the course of the match.
Paulinho came on in the 76th minute and scored in the 90th, while Arthur Gomes entered the fray just before additional time and scored 54 seconds later. Game-changing moves.
Spurs' best openings, contrastingly, fell to full-back Emerson Royal which spoke volumes about their non-existent frontline. Harry Kane and Richarlison shared a chance apiece. None for Son. You would be forgiven for forgetting he was even named on the teamsheet, such was his elusiveness.
Son's fall from grace has been quite remarkable considering he was the joint-Golden Boot winner last season. Low on confidence, certainly lacking in conviction, the 30-year-old perhaps needs to sit the next one out. His flair will undoubtedly return but Conte's faith is only serving to harm Spurs' fluidity up top in the short term.
Spurs taste defeat again - Opta stats
- Tottenham suffered their first defeat of the season against Sporting, while it's now four defeats in their last five Champions League games.
- Sporting have won their opening two games of a Champions League campaign for the first time in their history, while they've now won five of their last six group stage games in the competition.
- Tottenham have now lost each of their last three Champions League away games, as many defeats as in their previous 15 such games in the competition (W6 D6).
- There were just 54 seconds between Sporting substitute Arthur Gomes coming on and him scoring the second goal in the 93rd minute.
Tottenham's remaining Champions League fixtures
October 4: Eintracht Frankfurt (A) - kick-off 8pm
October 12: Eintracht Frankfurt (H) - kick-off 8pm
October 26: Sporting Lisbon (H) - kick-off 8pm
November 1: Marseille (A) - kick-off 8pm
What's next for Spurs?
Tottenham resume their Premier League campaign at home to Leicester, live on Sky Sports on Saturday, with coverage starting at 4.30pm on Sky Sports Premier League; kick-off 5.30pm.