Rennes looked all set to climb to fourth place after second-half goals by Julien Feret and Romain Alessandrini put them in the driving seat against Brest, but the visitors rallied with goals from Benoit Lesoimier and Charlison Benschop in the final 20 minutes.
Brest lost Ahmed Kantari to a second yellow card in the last minute following an altercation with the referee, but held on for a 2-2 draw.
Valenciennes needed a second-half own goal to earn a 1-1 draw against bottom-of-the-table Nancy at the Stade Marcel Picot.
Jordan Loties opened the scoring for the hosts just after the half-hour and that looked to be enough to get Jean Fernandez's side only a second league win of the season, until Massodio Haidara put through his own net 17 minutes from time.
Troyes came undone at the death for a second straight game as Dario Cvitanich earned Nice a point, cancelling out Stephane Darbion's close-range opener at the Stade de l'Aube.
The champions are not the same side that won the title last season, but they had little problem seeing off relegation-threatened Ajaccio thanks to goals from John Utaka, Remy Cabella and Younes Belhanda.
The mid-table visitors, who have been somewhat off the pace this season after finishing third in the last campaign, took the lead in the 62nd minute through Nolan Roux.
Sochaux hit back immediately through Tunisia international Yassin Mikari, although they had to hang on in the closing stages after Loic Poujol was dismissed for a second bookable offense.