Mbappe, who scored two and set up two last weekend against Lorient, struck both sides of the interval, just like Neymar, to take his league season tally to 20 and put PSG on 71 points from 31 games. They are 15 points ahead of second-placed Stade Rennais.
Clermont, who reduced the arrears through Jodel Dossou, are 17th on 28 points after their fifth defeat in a row.
In Clermont, PSG overcame mediocre first half to ultimately blow out their minnow hosts.
Neymar put them ahead after six minutes, firing home with a low crossed shot after being set up by Lionel Messi.
Messi also set up the second for Mbappe, who beat Arthur Desmas from inside the box with a clinical half volley in the 19th minute.
Clermont, however, hit back just before half-time when Saif-Eddine Khaoui's cross was met by Dossou, who found the back of the net with a right-footed effort from the penalty spot.
PSG were then unstoppable in the second half.
Neymar put them 3-1 up with a penalty after a foul on Mbappe in the 72nd minute, two minutes before the France international added a fourth, dribbling past the keeper after being set up by Neymar to tap the ball into the empty net.
Six minutes later, Mbappe was at it again, benefiting from a nice combination between Messi and Neymar to curl a shot into the top corner.
Seven minutes from time, Mbappe rushed into the area and his pass was collected by Neymar who coolly finished it off from close range.