Paris Saint-Germain were beaten 3-0 at Monaco on Sunday after a Wissam Ben Yedder double strike, as Neymar and Kylian Mbappe were both booked in a feisty Ligue 1 encounter.
PSG remain 12 points clear of second-placed Marseille at the top after the fourth league defeat of the season for Mauricio Pochettino's men, who have been shaken since being dumped out of the Champions League by Real Madrid.
Monaco captain Ben Yedder is now Ligue 1's top scorer with 17 goals after his 25th-minute tap-in from a rebound, and an 84th-minute penalty.
Ben Yedder also helped in the build-up for German striker Kevin Volland's goal for Monaco, making it 2-0 on 68 minutes in what was the real turning point of the game as PSG began to chase.
Mbappe and Neymar started for PSG and had a string of opportunities as the visitors enjoyed the lion's share of possession, but Lionel Messi was absent with the flu.
Mbappe said the bitterness of the Champions League defeat earlier this month was still felt at the club.
"We could win 8-0 and nobody would care, they'd just be thinking about the Champions League," he said.
"We need to remain professional, think of our families," said Mbappe, who was full of praise for his old club.
"They are a great team, who were playing in European competition," said the 23-year-old.
PSG captain Marquinhos described the defeat as a wake-up call.
"If we carry on like that the title will be in danger. We have been warned," he said.
"We came here to win and have fun, but that was a catastrophe."
PSG coach Pochettino said it was time his players picked themselves up.
"On a sporting level, that was shameful. We have to get over the disappointment of being eliminated from the Champions League," the Argentine said.
Monaco's Belgian coach Philippe Clement can also thank his goalkeeper Alexander Nuebel, who made important saves from Mbappe, Neymar and Achraf Hakimi.
Marseille defeated Champions League-chasing rivals Nice 2-1 at the Velodrome to reclaim second from Rennes, who hammered Metz 6-1 earlier in the day.
Arkadiusz Milik converted a penalty in first-half stoppage time and substitute Cedric Bakambu added a second on 89 minutes, with Mario Lemina grabbing a consolation goal for Nice.
Serhou Guirassy bagged a hat-trick for Rennes as Bruno Genesio's side recorded a fifth straight league win, bouncing back from Thursday's Europa Conference League exit at the hands of Leicester.
Martin Terrier struck the first two goals at Roazhon Park, while Hamari Traore was also on target as Rennes moved above Nice into third.
Strasbourg's Champions League push stalled again after a fourth draw in five outings following a goalless stalemate at Lorient, while Angers beat Brest 1-0 to end a seven-match losing run.
Bottom club Bordeaux lost 2-0 at home to nine-man Montpellier. Elye Wahi and Florent Mollet scored for the visitors who then had Nicolas Cozza and Mihailo Ristic sent off late in the first half, with Alberth Elis missing a penalty for Bordeaux
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