Nice secured their win with a 2-0 victory over 10-man Lyon on Friday night.
Nice captain Paul Baysse volleyed home the opener in the fifth minute at the Allianz Riviera. Jean-Michael Seri swept in the second after 76 minutes.
There was enough of a cushion for Mario Balotelli’s missed penalty not to have severe repercussions.
Lucien Favre's men are four points clear of Monaco who lost 3-1 at Toulouse.
"We beat a good Lyon team,” said Favre. “We will enjoy it but we'll carry on with our philosophy of going match by match. The league season is very long. It's good to be first and we've started the competition well but we have to keep on working."
Monaco’s setback came after they took the lead through Valere Germain.
Oscar Trejo levelled midway through the second half before Martin Braithwaite bagged a brace in the final 10 minutes to fire Toulouse up to third, ahead of PSG and to within two points of Monaco.
"In the second half our opponents were better than us,” said Monaco coach Leonardo Jardim. “You have to congratulate them for that. Toulouse are a good team with quality players."
PSG boss Unai Emery will be without several players, including Angel di Maria, Serge Aurier and Layvin Kurzawa, for the trip to bottom side Nancy. Edinson Cavani returns from international duty with Uruguay to lead the PSG line. Victory will take PSG second, four points behind Nice.