Fourth-placed Monaco thumped PSG 2-0 and offered to advice FC Barcelona in their Champions League return fixture against the Paris side.
Paris Saint-Germain suffered a Champions League hangover as a 2-0 home defeat against Kylian Mbappe's old side Monaco on Sunday damaged their Ligue 1 title hopes after Lille earlier reclaimed top spot.
Sofiane Diop and Guillermo Maripan scored to give Monaco the points as they stretched their unbeaten run to 11 games and moved to within two points of their opponents, who sit in third place.
Monaco have managed to win all the six points of the year on offer against PSG for the first time since 09-10. "Barcelona, if you need advice, send us a DM," the club's social media account posted on Twitter.
"We were not at the level we need to be at to win, and as coach I take responsibility for that," said coach Mauricio Pochettino, who left Marco Verratti on the bench at kick-off in the only change from the Barcelona game.
"We spoke about the importance of maintaining our concentration levels, but we can't exactly replicate our performance from one evening to the next."
There is now a genuine chance that PSG will miss out on the Ligue 1 title for the first time since Mbappe's Monaco pipped them in 2017.
Almost exactly five years to the day after he scored his first Ligue 1 goal as a 17-year-old for the principality side, Mbappe was kept quiet by the Monaco defence, while Neymar watched from the stands as he continues to recover from injury.