There was no place in the starting line-up or on the bench for record signing Neymar, who is said to be unsettled in France and has been linked with Barcelona and Real Madrid this summer, but he was nonetheless the focus of attention for a section of home fans who made clear their feelings towards the Brazil star.
PSG, who won their second straight league crown last season by 16 points, were soon into their stride this term as Julian Draxler's shot was blocked and Mbappe's effort was well saved by Nimes goalkeeper Paul Bernardoni.
Nimes midfielder Florian Miguel went close to giving the visitors a surprise lead when his header flew inches wide, but team-mate Pablo Martinez handled in the penalty area soon after.
The penalty was confirmed by the video assistant referee and Cavani made no mistake, sending his spot-kick into the bottom-left corner of Bernardoni's net.
Pablo Sarabia forced Bernardoni into another save and Cavani spurned a chance to extend PSG's lead from close range before the break.
The hosts did make it 2-0 with their first effort on goal early in the second period, however, Mbappe applying a neat finish from inside the box after being set up by Juan Bernat.
Thomas Tuchel's side put the game beyond the visitors in the 69th minute. Mbappe was this time the provider and Di Maria buried a low finish from 10 yards.
Mbappe, twice, and Cavani both squandered further opportunities as PSG pressed for a fourth goal, while Nimes went close to a consolation in the closing stages through Antonin Bobichon and Renaud Ripart.