Tammy Abraham grabbed a birthday goal and Willian marked his 300th Chelsea appearance with the second as Chelsea won in Lille.
Abraham, expected to earn an England call-up today, registered his first Champions League goal before Lille equalised through their own exciting young striker, Victor Osimhen.
But Willian's late volley secured a crucial first three points for Frank Lampard's side in Group H.
Lampard had played down the significance of this match but after dropping all three points to Valencia at home two weeks ago, and with a trip to Ajax next up, the margin for error would have got a lot smaller without a victory.
Lampard was able to recall a fit-again N'Golo Kante but there was no place in the squad for Ross Barkley following his Sunday night row with a taxi driver in Liverpool.
Much has been made of Chelsea's lack of experience - Lampard had four academy graduates in his side - but Lille themselves have an average age of less than 24.
Osimhen was already troubling the Chelsea defence and when Kurt Zouma's sliced clearance looped towards the 20-year-old, goalkeeper Kepa Arrizabalaga had to come out of his area to head clear.
Abraham celebrated his 22nd birthday with a goal in the 22nd minute after Marcos Alonso, in an advanced position down the left, laid the ball back to Fikayo Tomori.
The young defender launched it into the area where Abraham, just onside, was able to control the ball, spin and place it beyond Lille keeper Mike Maignan.
Stung into action, Lille looked to hit back straight away and Kepa had to get down low to his right to claw out a curling effort from Luiz Araujo.
But Kepa could do nothing to prevent an unmarked Osimhen from heading in at the far post from a corner to equalise.
Nigeria will lose out on Abraham once he makes his competitive debut for England, but the country's attack looks in safe hands with Osimhen.
Chelsea pressed for a second before half-time but Alonso curled a free-kick too high and headed a Mount cross over before Jorginho's effort clipped the outside of a post.
The visitors were almost undone at another corner after the break, Benjamin Andre in yards of space when he glanced a header across goal and narrowly wide.
Osimhen showed his rawness when put through in the inside right channel, opting to shoot when a ball across goal looked the better option, and blazed over.
That was a let-off for Chelsea, but they nearly let Lille off the hook when Abraham teed up Mount who hooked his shot wide.
However, when substitute Callum Hudson-Odoi got free down the left and lifted the ball towards with far post, Willian struck a volley into the ground and over Maignan.
There was still time for Kepa to almost gift Lille another equaliser when he sliced a clearance straight at Boubakary Soumare, but the keeper saved at his feet to ensure Chelsea got their European campaign up and running.