Montpellier was already behind when goalkeeper Dimitry Bertaud was sent off in the 17th minute to end any hopes of being competitive.
Pablo Sarabia had scored a fine eighth-minute opener, with PSG going on to net twice in the final five minutes of the first half through Angel Di Maria scoring and a comical Daniel Congre own goal.
Thomas Tuchel's men kept a fifth consecutive clean sheet as they went a 19th straight match without losing, with second-half strikes from Kylian Mbappe and Layvin Kurzawa adding gloss to the victory prior to a late sending off for Montpellier's Joris Chotard.
PSG thought it had scored a brilliant team opener only for Mbappe to be ruled offside before setting up Sarabia.
But Sarabia was not to be denied as he latched on to a loose ball in the hosts' next attack and curled a magnificent 25-yard finish over Bertaud.
Montpellier's hopes were all but over when Bertaud was sent off as he charged out of his box and was adjudged to have handled when saving an Mbappe effort. Montpellier protested furiously but there would be no VAR (video assistant referee) reprieve.
An angry Neymar was booked for dissent but he was smiling soon after when Di Maria smoothly chipped his finish over sub keeper Matis Carvalho after a neat one-two with Sarabia.
It was three in bizarre fashion just before the break as a Di Maria corner was sliced by Teji Savanier as he attempted to clear and it bounced in off the head of a helpless Congre.
Neymar had limped down the tunnel after a challenge from Arnaud Souquet just before the break, but there was relief for the home fans when he re-emerged for the second half and the Brazil star almost made it four only to be denied by Carvalho.
Mbappe's left-footed strike rebounded off the post but the World Cup winner did get his goal on 57 minutes when he rounded Carvalho and tapped in having been found by Neymar.
Seven minutes later it was Kurzawa, having remained in Paris after being linked with a January transfer, who swept in his first goal since striking against Montpellier a year ago.
Three minutes from time, Chotard got a second yellow card for a rash foul on Presnel Kimpembe to add salt to Montpellier's wounds, although there was some relief when PSG's Edinson Cavani was denied a headed sixth for a marginal offside.