Lille moved three points behind second-placed Marseille, who will look for a seventh straight win when they travel to Metz on Saturday (Sunday AEDT).

Sanches latched onto a superb flick from lively forward Jonathan Ikone, accelerated down the left and cut outside a defender before thumping a low shot into the bottom corner in the 84th minute.

It was the kind of goal Lille hoped for when spending 20 million euros ($A32.3 million) during the off-season to sign the 22-year-old Portugal international from Bayern Munich, making him the northern French club's record signing.

Victor Osimhen had a penalty well saved by Montpellier goalkeeper Geronimo Rulli moments after Sanches' goal.

Osimhen's run led to Lille's opening goal from the penalty spot in the 40th, when Rulli rushed rashly off his line and clattered into the Nigeria striker. Ikone sent Rulli the wrong way from the spot. But the France forward did not celebrate, having previously played for Montpellier on loan from Paris Saint-Germain.

It was the first penalty conceded by Montpellier this season, leaving defending champions PSG as the only side not to concede one. For Lille it was a league-leading sixth spot-kick.

Two Montpellier players were involved in a freak first-half injury as Teji Savanier headed the ball straight into the face of his 18-year-old teammate Joris Chotard, causing blood to pour from his nose.

The visitors equalised in the 74th when midfielder Florent Mollet expertly headed on a cross from the right to unmarked striker Andy Delort at the back post.

Delort then missed a chance to put Montpellier ahead before Sanches decided the match.

Australian Associated Press