The hosts were the first to threaten when Divock Origi picked up the ball on the right side of the box, but his subsequent low shot was saved by the keeper.
The hosts took the lead midway through the first half when Florent Balmont picked out Salomon Kalou with a cross, and the former Chelsea winger tucked his header into the top corner to break the deadlock.
Lille came close to doubling their advantage shortly before the half-hour mark as Idrissa Gueye let fly from 25 yards, but his effort fizzed narrowly wide.
Kalou came within inches of doubling his personal tally for the night just after the hour mark when he struck the post with an effort from just outside the area.
The visitors had a rare shot on target in the 65th minute when Cheick Diabate let fly from 25 yards, but Enyeama got down well to make the save.
It was 2-0 just three minutes later as Mendes converted from a couple of yards out to double his side's lead and put them well on the way to gaining all three points.
Lille set about looking to restore their two-goal advantage and almost managed it when Marko Basa met a cross just outside the six-yard box, but he couldn't keep his header down.
They had a glorious chance to make it 3-1 in the dying stages when they were awarded a penalty, but Kalou saw his spot kick saved as the hosts were forced to settle for a 2-1 win that takes them seven points clear of fourth.