A 1-0 loss at Caen before the international break saw Nice's lead at the top trimmed to three points, and they could find themselves knocked from the summit with Monaco visiting bottom side Lorient on Friday.
Nice's staying power will be sorely tested with a run of 10 matches in 31 days to finish the year, starting with Sunday's trip to Saint-Etienne, who are unbeaten at home this season.
"We had the break to clear our minds. Saint-Etienne will be a big match. It's our job to eradicate the bad things from the last few games. We want to restart well," midfielder Wylan Cyprien told Canal+ Sport.
Monaco underlined their burgeoning ambitions with a 6-0 thumping of Nancy last time out and will hope to follow that performance with another win at Lorient, ahead of Tuesday's Champions League tie at home to Tottenham Hotspur.
"Things are going well but you have to know how to keep it going. The difference between great players and the others is being able to maintain your best level each match," said coach Leonardo Jardim.
"The game before the Champions League is always important to win, both for confidence and to maintain the momentum," he added, knowing his side can punch their ticket to the last 16 in Europe with a draw against Spurs.
However, midfielder Tiemoue Bakayoko warned the appointment of former Marseille and France defender Bernard Casoni as the new Lorient coach could spark a reaction from the struggling Brittany club.
"It's always tough against Lorient. The cards are dealt over again with a new coach," said Bakayoko.
Motta heading for exit
Despite the growing pains under new boss Unai Emery, four-time reigning champions PSG could also climb above Nice with a victory over Nantes at the Parc des Princes on Saturday.
"The fact is that we're third in the league and our start to the season hasn't been as good as we had hoped it would be," Emery wrote recently in an open letter to the club's fans on his website.
"But the progress the team has made reinforces our optimism. We're aware that it's tough to win, then win again and then keep on winning, and we know that Ligue 1 is a competitive championship."
The Spaniard will be without midfielder Adrien Rabiot for three weeks after he tore his hamstring while making his international debut for France in midweek, while Thiago Motta plans to leave PSG at the end of the season.
"PSG is like my home and I've always given everything to win and help move the project along," the 34-year-old Motta told Italian daily Gazzetta dello Sport.
"That's why I believe it will be my last season as a player in Paris."
PSG face Arsenal in London next Wednesday with top spot in Champions League Group A at stake, while Lyon travel to Dinamo Zagreb next week bidding to prolong their Champions League adventure.
On Friday night they visit a Lille team languishing in the bottom three, although Nabil Fekir is suspended for the trip north with Rachid Ghezzal out injured and Clement Grenier a doubt.
Marseille host Caen on Sunday still searching for their first win under new coach Rudi Garcia.
Fixtures (all times GMT)
Lorient v Monaco (1800), Lille v Lyon (1945)
Paris Saint-Germain v Nantes (1600), Bastia v Montpellier, Nancy v Dijon, Rennes v Angers, Toulouse v Metz (all 1900)
Guingamp v Bordeaux (1400), Marseille v Caen (1600), Saint-Etienne v Nice (1945)