Monaco rode on a Wissam Ben Yedder double to beat Paris Saint-Germain 3-0, in a feisty Ligue 1 encounter that saw both Neymar and Kylian Mbappe booked.
PSG, however, remains 15 points clear of second-placed Marseille at the top of Ligue 1 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.
Nice can close the gap to 12 points if it beats Marseille in Sunday's late Ligue 1 game.
Monaco captain Ben Yedder is now Ligue 1's top scorer with 18 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.
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, playing in European competition," said the 23-year-old.
Monaco's Belgian coach Philippe Clement can also thank his 'keeper Alexander Nuebel, who made important saves from Mbappe, Neymar and the marauding Moroccan Achraf Hakimi.