Monaco dropped two valuable points in the race to catch Ligue 1 leaders Paris St Germain as Lille forced a 1-1 draw at Stade Louis II.
Mounir Obbadi fired the hosts into an early lead but Divock Origi had dragged Lille back into the game by half-time and Monaco were unable to find a winner after the break.
The result may prove crucial in the title race as PSG now hold a 10-point advantage over the principality club heading into the eight-game run-in, while Lille sit three points clear of St Etienne in third place.
Claudio Ranieri's hosts found themselves a goal to the good in the eighth minute after Dimitar Berbatov released Valerie Germain. His cutback found Obbadi, who side-footed the hosts into an early lead.
Despite the exciting opening, Jeremy Toulalan's effort from the edge of the area ended up on the wrong side of a post to sum up a quiet 30 minutes.
Monaco goalkeeper Daniel Subasic was finally called into action on 32 minutes when Idrissa Gueye hit the target with an acrobatic volley, but his effort failed to trouble the Croatian.
However, only five minutes later Lille went one better when Salomon Kalou found Ryan Mendes on the right and his delivery was turned home at the back post by young Belgian striker Origi.
Monaco's lacklustre first-half performance prompted Ranieri into a change, Argentinian youngster Lucas Ocampos being introduced, but it was Lille who almost took the lead just minutes after the break.
Kalou's superb ball in behind the hosts' defense found Jonathan Delaplace but, just when it seemed he was likely to add Lille's second, Subasic came off his line to make a crucial save.
Monaco responded and both Ricardo Carvalho and Ocampos went close with efforts as both sides showed signs of raising their game in front of the onlooking France manager Didier Deschamps.
Berbatov was the next to threaten with 20 minutes left to play but the former Manchester United forward headed just over the bar from a corner as the draw looked more and more likely.
Despite some late huffing and puffing, which saw a Kalou effort on goal go out for a throw-in, neither side showed the necessary quality to grab the winner and Monaco fell even further behind PSG.
