Didier Deschamps's side, who retained their League Cup title last Saturday, have 61 points to Lille's 60 after the northern side were held to a 1-1 draw on Sunday. Lille had been top of the table since December.
Ghana striker Andre Ayew bagged a hat-trick while younger brother Jordan scored the other goal.
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With six games left, Olympique Lyon stayed in the title race after a last-gap Yoann Gourcuff goal earned them a 3-2 home win against Montpellier.
The seven-times French champions are in third place, five points off the pace.
At Marseille's Stade Velodrome, the hosts went in front after 30 minutes when Nice keeper David Ospina released a routine cross in the path of Andre Ayew, who fired home from five yards.
The visitors reacted three minutes from the break, with Abdou Traore benefiting from a scramble in front of the goal to level from close range.
Ayew was on target again on the hour to latch onto a cross from his younger brother Jordan, who had just come off the bench, and double the tally.
MISSED PENALTY
Jordan was then on the receiving end of Rod Fanni's pass to make it three with a delicate curled shot in the 78th minute.
After Habib Bamogo missed a penalty for Nice in the 85th minute, Andre Ayew put the result beyond doubt with a header from a perfectly weighted cross by Fanni.
Former Marseille defender Renato Civelli headed home to reduce the arrears in stoppage time.
"It was not all perfect but we expected a tough game after having played the League Cup final on Saturday," Deschamps told Canal Plus television.
"We will savour this win but not for long as we're already playing again on Sunday."
France playmaker Gourcuff, who has been having a below-par season and was left on the bench for the game, eventually came on to give Lyon a deserved victory at their Gerland stadium.
Ederson unleashed a powerful long drive into the top corner after 23 minutes, only for Montpellier striker Olivier Giroud to equalise six minutes later with a fine half-volley.
Ten minutes into the second half, Lisandro Lopez put Lyon ahead again with a goal from close range after being perfectly set up by fellow striker Bafetimbi Gomis.
Souleymane Camara made it 2-2 five minutes from time as he poked the ball home after Hugo Lloris failed to block a Bengali Fode Koita shot.
But Gourcuff, who had replaced Gomis in the 87th minute, converted a Lisandro cross in the 90th as Lyon kept their title hopes alive.
