Lille were left hanging on to a Champions League place by a single point following their 1-0 defeat at Nice on Sunday.
Later, former multiple champions Lyon fell 2-0 at Rennes and Marseille were held 2-2 by Toulouse at the Velodrome.
Saint-Etienne's 3-0 success over struggling Valenciennes on Saturday had put the pressure on Lille but the 2011 champions failed to respond.
Former Paris Saint-Germain forward Mathieu Bodmer scored the only goal with a cute back-heel in first half stoppage time, although there was a suspicion of offside.
The defeat could have been worse for Lille but for Rio Mavuba clearing a Dario Cvitanich header off the line and Idrissa Gueye getting away with what appeared a blatant handball inside the Lille box.
Lille coach Rene Girard said: "We were inefficient, that sums up the way we played against a Nice side that appeared vulnerable.
"They didn't really put us in danger, but we conceded a goal at the worst moment."
At the turn of the year, Lille were challenging the top two, PSG and Monaco, but they have now dropped to 13 points off the summit after earning just two points from their last five matches.
"I don't seen any option for us but to work, the boys are already working well, but we must be vigilant and careful," Girard added.
Marseille remained in fifth, on 36 points, after their stalemate at home.
Twice Marseille went ahead, through goals by Dimitri Payet and Mathieu Valbuena, and twice they were pegged back.
Toulouse striker Wissam Ben Yadder levelled on 11 minutes with Serge Aurier ensuring they went home with a point on the hour.
Lyon, who pitched up seeking a fourth straight league win, had a torrid time of it at Rennes.
They went down a man when Samuel Umtiti was red carded for an ill-judged tackle on Romain Alessandrini three minutes from the interval.
Rennes were already leading at that stage thanks to Cedric Hountondji's 22nd minute header and new signing, Swedish forward Ola Toivonen, doubled up with less than half an hour left.
Lyon manager Remi Garde reflected: "I'm disappointed that we didn't get any points but I'm not worried because I believe we deserved better."