An own goal from Gelson Fernandes opened the scoring for the champions, then a defensive error paved the way for Edinson Cavani to net the second.
Following the break, PSG raced through the gears and doubled their goal tally with Adrien Rabiot and Marco Verratti netting.
The only big change from the hosts was Kevin Trapp replacing Alphonse Aréola between the sticks due to injury.
Meanwhile, Rennes welcomed Yoann Gourcuff back with star man Benjamin André dropping out of the midfield due to suspension.
Two gifts set hosts up after tough start
It was the travelling Bretons who started the brightest of the two teams, playing a high attacking line and put their opponents under unexpected early pressure.
The first chance of the game fell to Paul-Georges Ntep who tested Trapp at his near post, but the stand-in stopper saved the effort unconvincingly.
PSG grew into the game as the clock ticked on and were denied a clear goal scoring opportunity on 21 minutes when Fernandes used his hands to stop a Cavani header from going into the net.
After 10 minutes, lightning struck twice with Cavani heading once again at goal, this time Benoit Costil parrying the ball off the arm of Fernandes before bouncing over the line to put PSG in front.
Two minutes before the regulatory 45, PSG added to their lead with a goal that Cavani could claim without any doubt.
A slack pass from Pedro Mendes to the scorer allowed him to curl a precise shot over Costil.
Unfortunately for the Parisians, the Uruguayan injured himself in the process of shooting and had to be replaced by Jesé Rodriguez before the half time whistle.
Comfortable second period with no chance of a comeback
The second half started pretty scrappy with both teams conceding early fouls and resulted in several bookings dished out by referee Amaury Delerue.
It took a while for the first big chance of the half to present itself when Serge Aurier rattled the crossbar from well out, leaving Costil rooted to the spot.
However, only a minute later, Rabiot would try his own luck from distance and be rewarded with the third goal of the match.
Some would say that Costil should have done better to keep the shot out, however, on reflection, the ball dipped at just the right moment to avoid the keeper's attempt at a save.
As the game played out, PSG turned on the style for their fans and played some stunning passing play which Rennes couldn't keep up with.
After another unmistakable attack, PSG got their fourth and final of the match when Veratti smacked a volley from the penalty spot into the bottom right of the net.
The win for PSG puts them within three points of Nice who lost their first match of the season at SM Caen.
Rennes stay in fifth place, a point behind Guingamp on fourth.
The Bretons host revitalized Toulouse at Roazhon Park after the international break while host Rennes' bitter rivals FC Nantes at the Parc des Princes.
Rennes will need to dust themselves down during the break as a defeat to Toulouse could put their European ambitions at an early risk, whereas PSG will need to cope with life without Cavani in a bid to regain their league crown.