The result moved Monaco into second place on 47 points, one point above Olympique de Marseille who visit mid-table Clermont later on Saturday. PSG suffered their third loss in the league this season but remain on top with 54 points from 23 matches.
Aleksandar Golovin opened the scoring in the fourth minute after PSG failed to clear, after midfielder side-footing home Ben Yedder past three defenders to set up the shot.
Monaco doubled the lead after 14 minutes, after fine work from Crepin Diatta, who forced inexperienced 17-year-old defender El Chadel Bissiabu into an error, allowing Ben Yedder to slide the ball past goalkeeper Gianluigi Donnarumma.