Mevlut Erdinc's last-gasp equaliser denied champions Lille victory and earned 10-man Rennes a point from a 1-1 draw at the Stade de la Route de Lorient.
Aurelien Chedjou looked to have set the third-placed visitors on course for an away win when he opened the scoring five minutes before half-time - moments after the hosts had had Onyekachi Apam sent off.
But Les Rouges et Noirs never gave up and got their reward in the final minute when Erdinc's goal salvaged a draw.
LOSC headed into the game looking for a third straight win to boost hopes of retaining the title, but it was the home team who were in the ascendancy in the early stages.
Jean-Armel Kana-Biyik found himself one-on-one with Mickael Landreau from Julien Feret's through-ball after 10 minutes, but the goalkeeper's right foot kept out the striker's effort.
Landreau again came to his side's rescue three minutes later to push Kevin Theophile-Catherine's powerful right-footed shot away for a corner following a neat back-heeled pass from Jonathan Pitroipa.
Rennes' hopes suffered a blow seven minutes before the interval, however, when Apam saw red for two bookable offences in the space of a minute, the first on Nolan Roux and the second on Joe Cole.
Things then got worse for the hosts when, following the foul on Cole, Benoit Pedretti swung in the free-kick and Chedjou directed his header beyond Benoit Costil.
Rennes had a couple of chances to equalise early in the second half, but Landreau gathered Jires Kembo Ekoko's blast at the second attempt and then Vincent Pajot took the ball off the toe of Erdinc only to fire wide with just the keeper to beat.
Cole almost doubled Lille's advantage midway through the second half, but Costil dived to palm the Englishman's right-footed shot away for a corner.
The 10 men were continuing to test their visitors but struggled to find a way past Landreau. Romain Danze burst down the right and crossed for Yann M'Vila, but his first-time shot sailed into the stands.
Costil then made a brilliant double save two minutes from time to keep his side only one goal down, parrying substitute Ireneusz Jelen's effort and the follow-up from Benoit Pedretti.
And Lille were soon made to rue those misses as, in the final minute, Kana-Biyik launched the ball into the box and an unmarked Erdinc made no mistake with a clinical right-footed finish at the far post.
