Rennes, four days after firing coach Habib Beye, stunned Paris Saint-Germain 3-1 on Friday, snapping the defending champions' seven-match winning run in Ligue 1.
Second-placed Lens can now leapfrog the champions and retake top spot on Saturday if they beat Paris FC in the capital.
PSG started brightly, with Ousmane Dembele and Desire Doue carving openings to no avail.
Rennes fired Beye on Monday and promoted his assistant Sebastien Tambouret, and the same players who had lost four games on the bounce seemed transformed.
Jordanian forward Mousa Al-Tamari bagged the opener, unleashing a fierce strike into the bottom corner on 34 minutes.
Esteban Lepaul headed the second from a corner in the 69th minute, only for Dembele to pull a goal back two minutes later when he turned home a deflected cross.
⌛️ It ends in defeat tonight.#SRFCPSG I @Ligue1_ENG pic.twitter.com/pVKE3UYlIE
— Paris Saint-Germain (@PSG_English) February 13, 2026
PSG boss Luis Enrique hauled off Doue and Khvicha Kvaratskhelia for Bradley Barcola and Lee Kang-in, possibly with the midweek Champions League play-off round first leg at Monaco in mind.
Substitute Rennes striker Breel Embolo thumped in the third, decisive Rennes goal with nine minutes left to secure a famous win and lift them to fifth in the table.
Despite scoring his seventh goal in ten matches Dembele sounded a wake up call to his teammates.
"We need to win this kind of match. We need to play as a team, not as individuals," the current Ballon d'Or Dembele said.
"We need to put more desire into it. We have to play for Paris-Saint-Germain to win matches, because if we play alone on the pitch, it won't go well, we won't win the titles we want."
The former Dortmund and Barcelona man praised Rennes, the club where he came to prominence a decade ago.
"Rennes had a very good match," he said.
Luis Enrique picked Matvei Safonov over Lucas Chevalier here and the Russian 'keeper was unsighted for Al-Tamari's opener.
But central defender Willian Pacho had failed to challenge, while his partner Illia Zabarnyi was sluggish on the two other goals.
PSG's opponents in the first Champions League knockout round Monaco, beat Nantes 3-1 in Friday's late match.