Kylian Mbappe had a goal ruled out for offside while a subdued Lionel Messi also failed to find the target as Paris Saint-Germain's march towards another Ligue 1 title was slowed on Sunday after a 2-0 defeat at home to Rennes.
Marseille's 2-1 win away to Reims saw them close the gap on French leaders PSG to seven points with 10 games remaining.
Mbappe thought he had struck his 20th Ligue 1 goal of the campaign before it was chalked off. Karl Toko-Ekambi put Rennes in front with a magnificent strike right on half time.
Arnaud Kalimuendo made it 2-0 three minutes after the restart against his former club, as PSG – faced with a defensive injury crisis – slumped to a first home league defeat of the campaign.
It is the Parisians' fourth Ligue 1 loss this season, all of them in 2023, and the second time they have been beaten by Rennes. They also lost when the teams last met in Brittany in January.
"A defeat is always upsetting. Obviously I can't be happy with the way the match went but in the context, with the number of players we had out, we knew we were going to have difficult moments in defence," said PSG coach Christophe Galtier.
PSG only have a ninth Ligue 1 title in 11 seasons left to play for after being knocked out of the Champions League in the last 16 by Bayern Munich.
Achraf Hakimi, Presnel Kimpembe, Marquinhos, Sergio Ramos and Nordi Mukiele were all sidelined, leaving an almost unrecognisable back line featuring 17-year-old El Chadaille Bitshiabu. The Parisians were also unable to call on star forward Neymar, with the Brazilian ruled out for the rest of the season injured.
Galtier has insisted that the prospect of what would be a French record 11th top-flight title is sufficient motivation for his team, but their performance indicated otherwise.
"The objective is to win the league. Will this defeat mean the board will consider my future? Maybe. But everything needs to be put into context," Galtier added when asked about his position.
"There are no excuses but there are reasons for it."
The result allowed Rennes to reclaim fifth place from Lille in the fight for European qualification.
"To beat Paris twice in the same season says something about us. If we are capable of taking six points out of six against such a team, it means we have progress to make so we can do that in 90 percent of our matches," said Rennes coach Bruno Genesio.
Cameroon international Toko-Ekambi, brought up in Paris as a PSG fan, opened the scoring with an emphatic finish past goalkeeper Gianluigi Donnarumma after latching onto a long ball forward.
The home side were left facing an uphill struggle as they conceded again just after the interval, with Lesley Ugochukwu's low centre being turned in by Kalimuendo.
It was a seventh Ligue 1 goal of the campaign for the 21-year-old, who joined Rennes last summer from PSG after the capital club decided not to keep the forward who had performed well on loan at Lens last season.
Marseille moved back above Lens, who beat bottom side Angers 3-0 on Saturday, by coming from behind to end Reims' long unbeaten run.
Summer signing Alexis Sanchez scored both Marseille goals after Folarin Balogun had given the hosts a 13th-minute lead.
