Paris Saint-Germain blew a two-goal lead to lose 4-2 at relegation-threatened Bastia.
The reigning champions went into the game knowing a two-goal victory would see them leapfrog Lyon and Marseille and claim top spot in Ligue 1 for the first time this season.
Lucas gave PSG a 10th-minute lead and Adrien Rabiot doubled their advantage on the 20-minute mark.
But that was as good as it got for Laurent Blanc's men as a second-half brace from Julian Palmieri, after strikes from Ryad Boudebouz and Francois-Joseph Modesto, secured victory for Bastia.
Table toppers Marseille, who lost at Montpellier on Friday, still enjoy a three-point lead over fourth-placed Les Parisiens, but Lyon can replace them at the summit if they beat Toulouse on Sunday.
Saint Etienne, meanwhile, continued their impressive climb up the table with a 2-1 victory at Reims on Saturday night.
Goals either side of half-time from Yohan Mollo and Romain Hamouma put the visitors in control, and although a late own goal from Renaud Cohade sparked hopes of a fightback from Reims, their dreams were ended with the dismissal of Antoine Conte moments later.
St Etienne remain unbeaten in the league since early October, with Saturday's result lifting them up to third -- two points behind Marseille.
Lille secured back-to-back wins for the first time this season with a 1-0 victory over bottom side Caen.
A midweek win against Evian ensured Rene Girard's side a victorious return to Ligue 1 action and a first-half goal from Michael Frey sealed a second triumph in three days at the Stade Pierre-Mauroy.
Nice recorded just a second league win in three months as they shook off their goalscoring woes to beat Lorient 3-1.
Goals from Eric Bautheac, Alexy Bosetti and Carlos Eduardo secured all three points for Claude Puel's side after Benjamin Jeannot had given Lorient an early lead.
Paul-Georges Ntep's seventh goal of the season rescued a point for Rennes in a 1-1 draw at Evian, who took the lead through Adrien Thomasson.
Ola Toivonen missed a second-half penalty and several other chances to secure victory for Rennes.
Elsewhere, Christophe Mandanne and Claudio Beauvue were both on target as Guingamp extended their unbeaten run to five games with a 2-0 victory over Lens.