Paris Saint-Germain's hopes of retaining their Ligue 1 crown took a huge blow as Serhou Guirassy cancelled out Neymar's penalty to earn Rennes a 1-1 draw on Sunday.
With Lille beating Lens 3-0 on Friday, the pressure was on Mauricio Pochettino's side – knocked out of the Champions League in midweek – to respond in the title race.
But without the suspended Kylian Mbappe, PSG turned in a below-par performance, and only led thanks to Neymar's contentious first-half penalty.
Julian Draxler went close to doubling PSG's tally, yet their sluggishness finally proved costly as Guirassy headed home in the 70th minute, with Presnel Kimpembe's late red card compounding the champions' misery.
Ander Herrera sliced wide from Layvin Kurzawa's cut back, but PSG otherwise started poorly, and were almost punished when Guirassy chested in Jeremy Doku's shot, though the offside flag was rightly raised.
PSG were again fortunate just after the half-hour mark, Danilo Pereira bundling into Guirassy, who would have been through on goal, yet the officials failed to spot the foul.
Rennes' frustration with the officials was exacerbated on the stroke of half-time. Nayef Aguerd stuck out a leg to deny Kurzawa, who needed treatment and, after checking with the VAR, Ruddy Buquet harshly deemed it a foul.
Neymar's finish was far from convincing – Alfred Gomis guessing the right way, but failing to keep out the Brazil star's strike.
A fine first touch put Doku through immediately after the restart, only for the winger to direct a tame attempt straight at Keylor Navas.
Draxler is reportedly next in line for a new PSG deal, and the Germany international nearly produced a stunning goal before the hour, but after setting himself up with some wonderful touches, his on-the-turn volley flashed just wide.
Moise Kean went similarly close moments later, though PSG could only attack in flashes, and they were made to pay with 20 minutes remaining.
Benjamin Bourigeaud's corner was met by Guirassy, whose header clipped in off the upright, meaning Lille have one hand firmly on the trophy, and Kimpembe's red for a horrid lunge on Doku summed up a shambolic PSG display.