Paris: Ligue 1 leaders Lyon suffered their first defeat in 12 matches on Saturday, going down 2-1 at Lille to leave second-placed Paris Saint-Germain trailing by just two points with a game in hand.
Hubert Fournier`s side broke the deadlock after just three minutes when Corentin Tolisso converted a Nabil Fekir corner.
However, Idrissa Gueye clawed back an equaliser in the second half after a clever one-two with Rony Lopes.
And four minutes later, right on the hour mark, Manchester City loanee Lopes completed the turnaround with a nice strike from outside the box.
"A game is 90 minutes long. We can have regrets though, especially after our quality first half," coach Fournier said. "We could have been more ambitious instead of sitting back.
"It`s a big blow and I am angry because we missed a great opportunity. Every time we have the chance to widen the gap between us and the teams below us in the table, we slip up. I just hope we won`t regret it in the coming weeks."
Tolisso`s chance was Lyon`s first attempt on target but it seemed to force the Ligue 1 leaders into a coma.
The young midfielder netted his fifth of the season when he fired low past Vincent Enyeama following Fekir`s corner, but the Nigerian goalkeeper was never really troubled after that.
Meanwhile, LOSC never seemed able to trouble the leaders themselves in the first half as they looked to improve on a run of just one win in their last six league outings.
However, the second half saw a complete turnaround with Gueye sparking the hosts into life by stabbing the ball past Anthony Lopes in the Lyon goal after a quick one-two with Rony Lopes inside the area.
The Lyon `keeper was once again beaten soon after when his fellow countryman curled a superb shot low into the net from just outside the area.
Henri Bedimo and Christophe Jallet were both denied by Enyeama in the latter stages as Lyon pushed forward in search of an equaliser.
Their defeat gives Paris the chance to climb above OL into top spot if they can win at in-form Monaco on Sunday night.
OL remain four points ahead of third-placed Marseille, who suffered a shock 3-2 defeat at home to Caen on Friday after leading 2-0.
Meanwhile, Lille move provisionally up to eighth before the rest of the weekend`s games.