Willian marked his 300th appearance for Chelsea with the winner as Frank Lampard's side dug deep to beat Lille 2-1 and get off the mark in the Champions League.
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 their campaign, leaving their hopes of reaching the knockout stages already looking bleak.
Lille were crushed 3-0 away to Ajax in their opener in Europe but had won all four of their home games in Ligue 1 this term, given them cause for optimism.
Chelsea looked up for this game though, and Mason Mount should have done better than to blaze off target from 20 yards early on.
They found their breakthrough in the 22nd minute when Fikayo Tomori flighted a curling ball through the static Lille defence, and Abraham placed his shot past Maignan, who had been abandoned by his defence.
Mount threatened again but Chelsea then hit a rocky patch that proved costly. The warning signs had been there, with Luiz Araujo driving in from the right flank and forcing Kepa Arrizabalaga to show strong hands to prevent a firm left-footed shot finding the far corner.
Lille's leveller came in the 33rd minute, with Osimhen heading in powerfully from Jonathan Bamba's corner.
Jorginho struck the right post with a wickedly curling shot just before the break, while Benjamin Andre was a whisker away for the hosts with a header early in the second half.
Chelsea substitute Callum Hudson-Odoi showed flashes of attacking purpose and energy before Mount had a low shot saved.
Then Willian drew back his right boot and thumped the powerful volley to get the match-winning goal. Fate perhaps dictated it, Chelsea landing their first Champions League scalp of the Lampard era thanks to one of his former midfield colleagues.