Paris Saint-Germain's (PSG) quest towards another Ligue 1 title was hindered on Sunday as they went down 2-0 at home to Rennes, the second time Christophe Galtier's side have lost to the Brittany club in 2023.
Kylian Mbappe had an effort disallowed for offside before Karl Toko-Ekambi put Rennes in front with a magnificent strike in the final minute of the first half.
Arnaud Kalimuendo made it 2-0 three minutes after the restart against the club he left in the last close season, as PSG slumped to the first home league defeat of the campaign.
It is the Parisians' fourth Ligue 1 loss this season, all of them in 2023.
They lost away to Rennes when the teams last met in January.
The result means Marseille can cut PSG's lead at the top of the table to seven points if they win away to Reims in Sunday's late game.
Qatar-owned PSG were knocked out of the Champions League in the last 16 by Bayern Munich on March 9.
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.
Rennes, meanwhile, celebrated their fourth away win over Qatar-era PSG. The result allowed them to reclaim fifth place from Lille in the fight for European qualification.
The team finishing fifth will qualify for the Europa Conference League, with the top three going into the Champions League and fourth into the Europa League.
PSG were targeting a fifth straight domestic victory, but they have been severely hampered by injuries, with Neymar recovering from ankle surgery and their defence decimated.
Achraf Hakimi, Presnel Kimpembe, Marquinhos, Sergio Ramos and Nordi Mukiele were all side-lined, leaving an almost unrecognisable back line to take to the field, featuring 17-year-old El Chadaille Bitshiabu.
PSG have usually been able to rely on their attack for inspiration, but Mbappe was unable to add to his 19 league goals this season and Lionel Messi was denied by Steve Mandanda, the veteran Rennes goalkeeper, who was in fine form.
Cameroon international Toko-Ekambi, who was brought up in Paris as a PSG fan, opened the scoring in the 45th minute 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.
PSG are nine points clear at the top of the table from Lens who moved above Marseille into second with a 3-0 win over bottom side Angers on Saturday, in that match the Belgian international Lois Openda scored twice.