Monaco now have 71 points with eight games to play, although Paris stayed in their slipstream after the four-time defending champions came back from a goal down to beat Lyon 2-1.
Guardiola faces test of resolve after 'pathetic' City's Euro woe
Early season pace-setters Nice have 64 points after a 1-1 draw at Nantes on Saturday which put them four behind PSG while Lyon's loss left them 14 points outside the Champions League places.
Four days after edging Manchester City into the Champions League quarter-finals, Mbappe, who scored in both legs of the City win, ran Caen ragged.
Caen coach Patrice Garande said after the game Monaco had been better in every department, but singled out Mbappe for special praise.
Guardiola won't change philosophy despite failure in Monaco
"They have an absolute phenomenon up front -- he killed us on his own," Garande admitted. "We knew beforehand it was going to be a tough afternoon. We were deservedly beaten by a really, really great side."
The 18-year-old Mbappe got off the mark on 13 minutes when, after a swift exchange of passes, he ran through the defence into the box and sent the 'keeper the wrong way with a low hard shot.
Two days after being called up into the France squad for the first time, Mbappe proceeded to torment the Caen back-line into giving away a penalty converted by Fabinho on 49 minutes to make it 2-0.
He then headed the third off the underside of the bar late in the game for Monaco's 87th goal of the league season.
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