A second-half goal from Przemyslaw Frankowski earned Lens their first victory over Lille in 15 years as they moved up to provisional second place in Ligue 1 with a 1-0 win after a derby marred by crowd trouble on Saturday.
Frankowski's strike ended a 12-game winless streak for Lens against the French champions, who had beaten them 4-0 and 3-0 last season.
Lille, who have only one win this season, are 13th on five points.
"We had chances but we did not convert them. We play some good games but we lacked that killer instinct," Lille midfielder Benjamin Andre said.
The second half started late following a 30-minute suspension after some Lens supporters ran onto the pitch towards Lille's corner, where a brawl erupted. Riot police and stewards intervened before the game resumed under police supervision.
The game, which kicked off at 4 p.m. CET, resumed at 4.30 p.m. CET.
Lens, who rejoined Ligue 1 last season after five years in Ligue 2, had dominated the first half with Gael Kakuta and Florian Sotoca testing Ivo Grbic twice in a tense contest in which Lille threatened on the break.
But both sides lacked sharpness in the area.
Lens enjoyed possession and played some neat passing football, but Lille were the most dangerous side early in the second half with Burak Yilmaz coming close with a downward header.
In the 74th minute, Kakuta found Frankowski with a slick pass, and the Poland winger beat Grbic in clinical fashion with an angled shot.
The hosts thought they had a second five minutes later, but Wesley Said's strike was cancelled following a VAR review in which Kakuta was judged to be offside.
Nevertheless Lens held firm until the final whistle, which prompted wild celebrations in the stands.
"It's an incredible feeling that we can't explain. We are so proud, we did it for the fans. Last year we lacked experience and we were without the supporters. We were too emotional," Lens midfielder Seko Fofana said.