PSG had a long list of absentees, including Neymar, Angel Di Maria and Mauro Icardi at Stade des Costieres on Saturday (AEDT), yet still eased to a fifth consecutive victory.
Loick Landre gave the champion a helping hand when he was sent off against his former club for catching impressive debutant Rafinha with a high boot just 12 minutes in.
Mbappe opened the scoring in the first half and added his fourth goal in as many Ligue 1 games late on after Alessandro Florenzi nodded in the second, with Pablo Sarabia rounding out the scoring in the closing stages.
Florenzi also struck the woodwork twice, while Moise Kean hit the crossbar and ought to have marked his debut with at least one goal during a game that saw Baptiste Reynet prevent Nimes from suffering an even bigger hammering.
Leandro Paredes was forced off after he was caught by a Lucas Deaux, who was perhaps fortune to only be booked, so Ander Herrera made an early appearance off the bench.
Nimes was a man down soon after, though, when Landre was dismissed by busy referee Clement Turpin for rashly catching Rafinha.
Reynet produced a magnificent save to palm Herrera's downward header wide, but Mbappe rounded the keeper superbly before slotting home 32 minutes in after he was picked out by Rafinha.
Kean had already passed up a couple of opportunities before Reynet tipped his tame effort around the post when the striker should have scored, while Idrissa Gueye and Mbappe had headers saved before the break.
Nimes was chasing shadows and Florenzi volleyed against the post before nodding against the woodwork after Rafinha was replaced after an impressive bow.
Florenzi was on hand to head in a second from close range 13 minutes from time, though, and Mbappe clinically added a third before Sarabia drilled home to complete an emphatic victory.