The leaders, who dropped two points after a 2-2 home draw with Evian last Tuesday, gave a solid performance to reclaim the place PSG briefly held after defeating Valenciennes 4-3 on Sunday.
"Paris had put us under the pressure when they won. I expected my boys to give their answer on the pitch and they did," Montpellier coach Rene Girard told a news conference.
"Since the season began, we are here, at the top, we've been there from the start."
Lille, who still have a slight chance of retaining their crown and travel to Montpellier next weekend, are five points behind the leaders after they thrashed Caen 3-0 at home thanks to two goals from Tulio de Melo.
Their fifth consecutive win helped the defending champions secured their Champions League qualifying spot for next season. The top-two teams qualify for the Champions League group stage and the third move into the play-off round.
Montpellier looked nervous after they ended with nine men against Evian but they controlled the match at Rennes.
The hosts failed to score the opener when Jonathan Pitroipa's acrobatic volley hit the woodwork after 12 minutes.
Souleymane Camara, who missed a stoppage-time penalty against Evian, put Montpellier ahead in the 26th minute when he took advantage of a John Boye mistake to score from close range.
The leaders, who have never won the French title, then had the upper hand and doubled their lead seven minutes into the second half when a powerful Remi Cabella shot hit the post only to bounce off goalkeeper Benoit Costil's back and roll into the net.
HAZARD SHINES AGAIN
At Lille, now certain to end the season no lower than third as fourth-placed Olympique Lyon lie 11 points behind, De Melo scored the opener from the penalty spot in the 26th minute after keeper Alexis Thebaux challenged Eden Hazard on the edge of the box.
The Brazilian striker doubled the lead 10 minutes later when he headed home from a Dimitri Payet corner-kick.
Hazard, reportedly the target of several leading European clubs, shone again as he set up Payet for the third goal in the 60th minute.
Sochaux climbed out of the relegation zone when they beat Nancy 1-0 at home thanks to a late goal by Sebastien Roudet. Sochaux are 17th on 36 points, one ahead of Brest.
Auxerre fell to the bottom as they lost 4-2 at home to Bordeaux after failing to recover from the visitors' three goals in the first nine minutes.
Auxerre are on 34 points, two from safety, while Bordeaux moved up to seventh place on 55 points, two behind Rennes.
Saint-Etienne are level with Rennes after they were held to a 0-0 home draw by Olympique Marseille.
