Lille remain in fourth place, two points behind Monaco and Marseille, who play on Sunday.
New signing Anthony Lopes was in the Nantes goal. He joined after playing nearly 500 games for Lyon.
Lopes was beaten in the 41st minute when defender Gabriel Gudmundsson volleyed in the rebound after winger Remy Cabella's curler came back off the crossbar.
Promising French forward Matthis Abline equalised for 15th-placed Nantes with a penalty in the 70th.
Lyon moved up to fifth after beating rock-bottom Montpellier 1-0 thanks to a stoppage-time own goal from Khalil Fayad following a penalty box scramble.
Montpellier were unlucky to lose.
Midfielder Jordan Ferri hit the post for Montpellier early on against his former club.
Ferri also put the ball in the net early in the second half but the goal was ruled out following a video review.
Then, winger Wahbi Khazri's free kick was tipped over by Lyon goalkeeper Lucas Perri in the 83rd.
Earlier, Augustine Boakye got his first goals for Saint-Etienne and Norwegian coach Eirik Horneland celebrated his first game in charge of the club in a 3-1 win against Reims.
Boakye, a midfielder from Ghana, struck twice in the second half as Saint-Etienne snapped a run of three league defeats and moved up to 14th place. Horneland replaced Olivier Dall'Oglio, who was fired on December 14.
Japan's Keito Nakamura grabbed his seventh goal of the season to give Reims the lead approaching halftime.
Belgian forward Lucas Stassin made the game safe for Saint-Etienne late on.
Unbeaten leader Paris Saint-Germain were not in league action and face Monaco in the Champions Trophy on Sunday.
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