There was just a single change from the Parisans side that narrowly edged Angers last Saturday, with Mauro Icardi recalled for Moise Kean.
An energetic opening from the home side nearly resulted in the breakthrough through a move from the right-side by Leandro Paredes, but Neymar Junior couldn't profit from the back-post.
Montpellier's evening turned on 19 minutes when goalkeeper Jonas Omlin saw red for a lunging challenge on Kylian Mbappe, with the Video Assistant Referee (VAR) altering the on-field decision.
PSG made their dominance count when Mbappe took a ball towards the left in his stride to dink home, as an injury forced Florent Mollet to vacate for Joris Chotard on the side of Montpellier.
A goalkeeping change from PSG at the start of the second half saw Keylor Navas removed for Spaniard Sergio Rico.
Nevertheless, Neymar gave the hosts a second after a cutback from the right by Mbappe 60 minutes in found the Brazilian, who tapped home easily, before the floodgates opened minutes thereafter as Icardi charged into the centre of the area to send a ball from the right into the top-corner.
A fourth arrived as the closing quarter approached when Mbappe got his brace after getting on the end of a square ball from Icardi to finish off a flowing move.
Montpellier weren't out of danger as an outstanding overhead kick on the edge of the area from Layvin Kurzawa cracked the top of the crossbar but despite their healthy lead, Mauricio Pochettino's side still searched for more goals near the end but had to settle for four goals.