LOSC inflict defeat on Claudio Ranieri's men for the first time this season thanks to a memorable display from their Nigerian goalkeeperMonaco were beaten for the first time since their return to Ligue 1 after going down 2-0 away to Lille at the Stade Pierre-Mauroy.
LOSC keeper Vincent Enyeama produced a sensational performance in goal for the hosts as he kept out Radamel Falcao and his team-mates time and again, with a double from Nolan Roux proving enough to secure the points for Rene Girard's men.
The result sees Rene Girard's men leapfrog their opponents in the table and sees them stake a claim as genuine contenders in the French title race.
Nolan Roux put the hosts in front midway through the first half when he kneed home from Marko Basa's knock down from after the central defender connected with Florent Belmont's corner.
Claudio Ranieri's side dominated for large chunks of proceedings but couldn't find a way past an inspired Enyeama in les Dogues' goal and Lille hit their opponents on the counter in the second period as Salomon Kalou and Rio Mavuba combined to set up Roux for his second to seal the victory.
The principality outfit continued to search for a way back into the game but an incredible late double-stop from Enyeama to deny Radamel Falcao and Emmanuel Riviere typified the visitors as they were condemned to their first league defeat of the season.
After the game, Riviere paid tribute to the Lille shot-stopper and admitted his side hadn't done enough to merit the points.
"It was a tough game and we had a bad first half," conceded the striker when he spoke to Canal+ after the full-time whistle.
"Respect to the goalkeeper who has made some fantastic saves in the second half. LOSC deserve their victory. We now need to keep our heads up and work harder."