Paris Saint-Germain failed to capitalise on Montpellier's slip-up against Lorient after conceding an 87th-minute goal to draw 1-1 at bottom side Auxerre on Sunday in Ligue 1.
With Montpellier having gone down 2-1 at Lorient earlier in the day, PSG were bidding to draw level on points at the top of the table, but Anthony Le Tallec's late equaliser left them two points behind Montpellier with six games to play.
It was a problem of determination and concentration," said PSG coach Carlo Ancelotti, who started with record signing Javier Pastore on the bench. "We played too sloppily. If we want to win the championship, we won't do it playing like that. We have to completely change our attitude.
"I'm annoyed with the players. We have to react quickly. We've missed a big opportunity and I'm not happy."
After Jeremy Menez had grazed the post following a neat back-heel from Kevin Gameiro, PSG forward Nene broke the deadlock in the 23rd minute when he steered the ball past Olivier Sorin to claim his 14th league goal of the campaign.
Auxerre midfielder Kamel Chafni hit the post after wriggling through the PSG defence in the 53rd minute, while visiting goalkeeper Salvatore Sirigu had to produce a smart save to repel Dennis Oliech's header moments later.
Substitute Sylvain Armand almost scored an own goal with nine minutes to play before Auxerre's pressure finally told, with substitute Le Tallec tapping home after Sirigu had fumbled a low shot from Omar Kossoko. Despite striking a potentially pivotal blow in the title race, Auxerre remain five points adrift of safety.