Monaco condemned Mauricio Pochettino to his second defeat as Paris St-Germain head coach with a shock win at Parc des Princes in Ligue 1.
Sofiane Diop opened the scoring for the visitors in the sixth minute, heading home Ruben Aguilar’s header back across goal from Kevin Volland’s cross.
And Guillermo Maripan doubled the lead with a second-half side-footed finish after Ander Herrera failed to clear.
The hosts had just one shot on target as Monaco cantered to all three points.
In their first game since their impressive 4-1 win at Barcelona in the Champions League, PSG struggled to create clear-cut chances after Monaco’s early opener.
Niko Kovac’s side should have been 3-0 up on the hour mark as Volland headed wide when unmarked inside the six-yard box.
Despite dominating possession the champions tasted defeat for the fifth time in the league this season.
And the loss means they stay third, four points behind leaders Lille, who thrashed Lorient 4-1 on Sunday.
Kovac’s Monaco are fourth, now just two points behind Pochettino’s side.