Laurent Blanc's side lost for the first time in any competition this season thanks to late goals from Clarck N'Sikulu and Modou Sougou.
PSG wasted several chances to go ahead and defeat leaves them just a point ahead of Lille in the table.
St Etienne, meanwhile, saw their bid to move into the top four wrecked by out-of-form Rennes.
Les Verts had lost just once in their last six matches and if they had picked up a victory at the Stade de la Route de Lorient they could have moved above fourth-placed Marseille on goal difference.
However, 13th-placed Rennes claimed a 3-1 victory thanks to a brace from Silvio Romero and another from Romain Alessandrini, Mevlut Erdinc grabbing a late consolation.
Julien Faubert scored the winner as Bordeaux moved up to seventh following a 1-0 victory over Guingamp in a feisty clash at Stade du Roudourou.
The 30-year-old France defender netted midway through the first half as Les Girondins claimed their second successive league win following Saturday's 4-0 result over Ajaccio.
But their victory was soured by Lucas Orban's dismissal 10 minutes after the break before Claudiu Beauvue was sent off in the dying minutes for the away side, who have dropped to ninth in the table.
Maxime Barthelme and Vincent Aboubakar were on target as Lorient claimed their fourth successive win with a 2-0 result against nine-man Montpellier at Stade de la Mosson.
The win also sees Les Merlus record their seventh straight clean sheet in all competitions as Christian Gourcuff saw his side move up to 12th.
Hilton and Abdelhamid El Kaoutari saw red for Jean Fernandez's men in the dying minutes and the defeat leaves them just outside the relegation zone in 17th after a winless run of seven league games.
Eduardo's 82nd-minute equaliser earned Ajaccio a barely-deserved 1-1 draw against Bastia at an empty Stade Francois Coty.
No one was there to see Florian Raspentino open the scoring, nor Eduardo rescue a point, with both sets of supporters banned from attending following troubles in both matches last season.
Struggling Sochaux's quest for only their second victory of the season goes on after they slumped to a 2-0 home defeat at the hands of Reims.
Christopher Glombard opened the scoring early on following a defensive error and Prince Oniangue added a late second as 11th-placed Reims picked up their first win in four matches to halt their slide towards the relegation places.