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.
While Monaco remain in contention for a return to the Champions League, PSG find themselves a point behind Lyon in second and four points adrift of Lille, who retook top spot earlier on Sunday with a 4-1 win at Lorient.
It was a disappointing night for PSG as they failed to pick up where they left off in midweek, when they destroyed Barcelona in the first leg of their Champions League last-16 tie, Mbappe scoring a hat-trick in a 4-1 win.