Sporting Lisbon condemned Tottenham to their first defeat this season as Paulinho's last-gasp goal inspired a shock 2-0 win in the Champions League on Tuesday.
Antonio Conte's side paid the price for some sloppy finishing and two pieces of dismal defending in stoppage-time at the Jose Alvalade Stadium.
Richarlison, Harry Kane and Emerson Royal were all unable to beat Sporting keeper Antonio Adan, while Son Heung-min's goal-drought extended to eight games.
Tottenham were still on course for a point until the dramatic denouement as Paulinho headed home before Arthur Gomes danced through the defence to seal Sporting's second successive Group D victory.
It was a first loss in eight games in all competitions for Tottenham, putting a dampener on a fine run that included a 2-0 win against Marseille in their Champions League opener last week.
Tottenham will still expect to qualify for the knockout stages, but this defeat adds pressure on them to avoid another slip in their remaining group games.
With last weekend's Premier League match at Manchester City postponed following last week's death of Queen Elizabeth II, Tottenham looked rusty on their return to action.
After a minute's silence to pay tribute to the Queen, Sporting, who beat Eintracht Frankfurt in their opening game last week, wasted little time setting the tempo.
Sporting's Marcus Edwards was at Tottenham's Academy from the age of eight and earned comparisons with Lionel Messi from then boss Mauricio Pochettino.
But north London-born Edwards only made one appearance in a League Cup game in 2016 before being allowed to leave three years later.
The 23-year-old has been revitalised since moving Portugal, earning a transfer to Sporting in January this year.
Edwards, who scored against Frankfurt, quickly reminded Tottenham of what they let go as he launched an early raid that ended with Pedro Goncalves' shot forcing a good save from Hugo Lloris.
- Shell-shocked Spurs -
Edwards was one of several former Premier League players in Sporting's side and Trincao, latterly of Wolves, fired narrowly wide from the edge of the area.
Richarlison had scored his first Tottenham goals since his summer move from Everton in the win against Marseille and the Brazilian tested Adan with a header from Ivan Perisic's cross.
Fuelled by the chance to prove his point to Tottenham, Edwards carried Sporting's main threat.
Edwards looked every inch the Messi clone when he embarked on a brilliant burst through the heart of the Tottenham defence on the stroke of half-time.
After playing a one-two with Trincao, Edwards was just six yards from goal with only Lloris to beat but the Tottenham keeper made a good save.
Emerson wasted a good chance when he failed to beat Adan with a close-range shot from Kane's clever free-kick early in the second half.
Tottenham were beginning to heat up and Kane's thunderous drive forced a fine save from Adan before Richarlison fired narrowly wide.
Kane was inches away from converting Perisic's cross at the far post and Richarlison was off target with a headed chance.
Son's failure to score this term had led Conte to hint he wouldn't keep the South Korean in his starting line-up if the drought continued much longer.
It was another frustrating day for Son, who was substituted in the 72nd minute after drawing another blank.
Lloris looked to have saved Tottenham when he clawed away Pedro Porro's curling strike in stoppage-time.
But from the resulting corner, Paulinho got in front of Kane to head the decisive goal.
Tottenham were shell-shocked and Gomes came off the bench to mark his Champions League debut with a superb solo strike as he jinked through the defence to shoot past Lloris.