Lille came out the surprisingly stronger side against Ligue 1 third-placed Monaco after holding the Principality team 0-0 on Friday at the Stade Louis II.
Hosts Monaco, who beat Nice 2-1 last week, took a brief hold on top of the French league after just two games in the 2015-2016 season, though having failed to make back-to-back wins, reported Xinhua.
Thanks to their goalkeeper Vincent Enyeama, the visitors denied plenty of chances of Monaco in the first half, and even narrowly missed a second half score of themselves.
Monaco's Bernardo Silva had a header wide just 40 seconds into the second round game, while Nabil Dirar showed excellent control for a long ball but Enyeama blocked it with his legs.
Another superb save from the Lille goalie came late in the first half when Enyeama saved from a Joao Moutinho free kick.
Lille produced two quick chances after the break, as Baptiste Guillaume got on the end of some good passing but was denied on both occasions by Monaco keeper Danijel Subasic.
Monaco had one late chance as Ricardo Carvalho's header from a free-kick was brilliantly saved by Enyeama, but Lille squandered too when substitute Soualiho Meite missed a flick shot in stoppage time.