The Brazilian had a mostly quiet game but produced a rare moment of quality in the second half, cracking a powerful volley beyond Mike Maignan in the 77th minute to secure three points.
Tammy Abraham had earlier marked his 22nd birthday with his first Champions League goal, but Victor Osimhen headed Lille level by half-time.
The first half had been vibrant, but the level of both sides dipped in the second 45 minutes. Chelsea were happy to take the spoils by any means, however, having lost their opening Group H match to Valencia at Stamford Bridge.
Lille, meanwhile, have suffered back-to-back defeats at the start of its campaign, leaving its hopes of reaching the knockout stages looking bleak.