Match ends, Lille 1, Chelsea 2.
Willian's excellent second-half volley gave Chelsea victory over Lille in their second Champions League group stage match in France.
The Brazilian put away substitute Callum Hudson-Odoi's cross in the 77th minute after Victor Osimhen had cancelled out Tammy Abraham's opener.
Chelsea sit third in Group H following Ajax's 3-0 win over Valencia.
However, they have kept just one clean sheet in 11 games under manager Frank Lampard, and none away from home.
The Blues lined up in a 3-4-2-1 formation as Lampard handed starts to 19-year-old Reece James and Fikayo Tomori, 21.
Both impressed but Lille were a threat throughout, and came close on several occasions in the second half.
Goalscorer Osimhen, bought as a summer replacement for Arsenal-bound Nicolas Pepe, caused problems in the air and it was his header which brought Lille level only 11 minutes after Abraham had given Chelsea the lead.
Benjamin Andre's header was tipped past the post by Kepa Arrizabalaga, and the Chelsea keeper had a couple of nervous moments when he was forced to come out to the edge of the box to stop quick counter-attacks.
But Chelsea were the better side and deserved victory - Jorginho smacked the outside of the right post with a curling effort in the first half and Mason Mount was denied from close range after the break.
Abraham fighting for England spot
It was another test for Chelsea's young squad, with four players in the starting XI who had played in the Championship last season.
Abraham, who turned 22 on Wednesday, was one of those, having spent 2018-19 on loan at Aston Villa.
He has impressed hugely since his return to Stamford Bridge, netting seven goals in as many Premier League games and picking up an assist in the Uefa Super Cup defeat by Liverpool.
And he was on the scoresheet again in France, bringing down Tomori's diagonal cross with an exquisite touch before sorting out his feet and coolly slotting into the bottom right corner.
It was the first time since March 2012 that two Englishmen combined to score in the Champions League for Chelsea - the last when current boss Lampard set up John Terry - and Abraham will be hoping for a call-up to his country's senior side when the squad is named on Thursday.
James became the first teenager to start for Chelsea in the Champions League since Ruben Loftus-Cheek in 2015 and was a threat from right wing-back - delivering dangerous crosses and using his pace to exploit the space in behind.
And Tomori was excellent at the back, while also recording his assist.
Willian's experience proves decisive
In a season where Chelsea's youngsters have impressed, it was 31-year-old Willian who provided the quality needed to win in Europe.
The technique in his volley was exquisite as he watched 18-year-old Hudson-Odoi's cross fly onto his boot before he fired it into the ground and over the keeper.
The goal was his first in Europe since March, and his second in the space of five days after he netted against Brighton at Stamford Bridge.
It had taken him eight months to score in the Premier League, but he finished with a game-high six shots against the Seagulls.
Willian was a threat all evening in France too, whipping in dangerous crosses for Mount and Abraham before eventually scoring the winner.
"It's never an easy place to play and Willian scores a worldie - no surprise there," Abraham told BT Sport.
Man of the match - Willian
'Tomori was outstanding'
Chelsea boss Frank Lampard on BT Sport: "It feels really good. This was a really hard place to come, added to the pressure of not beating Valencia. And it was the first time for a few travelling in Europe.
"Tomori was outstanding again. He has to keep on with that. Now Ajax have set their stall out in the group. This gives us confidence and points. Now the hard work begins."
Abraham is a man in form - best of the stats
- Chelsea ended a run of four games without a Champions League win (D2 L2), picking up their first victory in the competition since November 2017 (4-0 v Qarabag).
- Lille are winless in their last nine home Champions League games (D3 L6), losing each of their last four.
- In the 68 games that Frank Lampard has managed Derby and Chelsea in all competitions, his teams have only kept a clean sheet in 22% of their matches (15 out of 68).
- Across all competitions, only Manchester City's Raheem Sterling (nine) has scored more goals for an English club than Chelsea's Abraham (eight) in 2019-20.
- Since making his Champions League debut for Chelsea in September 2013, Willian has been directly involved in more goals than any other player for the club (15 - 10 goals and five assists).
- 17Zeki Çelik
- 6José Fonte
- 21AndréSubstituted forRenato Sanchesat 69'minutes
- 11de Araújo Guimarães NetoSubstituted forda Silva Rochaat 75'minutes
- 10IkonéBooked at 44minsSubstituted forYaziciat 62'minutes
- 8da Silva Rocha
- 18Renato Sanches
- 24JamesBooked at 35minsSubstituted forHudson-Odoiat 67'minutes
- 10WillianSubstituted forPedroat 85'minutes
- 19MountSubstituted forKovacicat 87'minutes
- Aleksey Kulbakov
- Shots on Target
Second Half ends, Lille 1, Chelsea 2.
Foul by Pedro (Chelsea).
Reinildo (Lille) wins a free kick in the defensive half.
Foul by César Azpilicueta (Chelsea).
Jonathan Bamba (Lille) wins a free kick in the defensive half.
Pedro (Chelsea) wins a free kick in the attacking half.
Foul by Xeka (Lille).
Foul by Callum Hudson-Odoi (Chelsea).
Mehmet Zeki Çelik (Lille) wins a free kick in the defensive half.
Substitution, Chelsea. Mateo Kovacic replaces Mason Mount.
Callum Hudson-Odoi (Chelsea) wins a free kick in the defensive half.
Foul by Yusuf Yazici (Lille).
Corner, Lille. Conceded by César Azpilicueta.
Substitution, Chelsea. Pedro replaces Willian because of an injury.
Goal! Lille 1, Chelsea 2. Willian (Chelsea) right footed shot from the right side of the box to the high centre of the goal. Assisted by Callum Hudson-Odoi with a cross.
Substitution, Lille. Xeka replaces Luiz Araújo.
Foul by César Azpilicueta (Chelsea).
Victor Osimhen (Lille) wins a free kick in the defensive half.
Corner, Chelsea. Conceded by Mike Maignan.