Cesar Azpilicueta clenched his fists together in celebration as the final whistle sounded at Stamford Bridge. Chelsea's season has been all about their young players so far. On this occasion, however, it was fitting it was their captain's goal which made the difference.
This game had been billed as a test of character for the club's academy stars. A place in the Champions League last 16 was at stake and the pressure was on after a poor run of form. In the end, though, it was the older heads in the team who guided them through - albeit by a fine margin.
Frank Lampard knew it was a night for experience and it showed in his team selection. There were three changes from the 3-1 loss to Everton and each one saw a younger player replaced by an older one. In defence, Andreas Christensen and Reece James made way for Antonio Rudiger and Emerson. In midfield, Mason Mount dropped out for Jorginho.
Rudiger's return was particularly welcome. The Germany defender has been missed this season, particularly at Goodison Park on Sunday, where Christensen and Zouma were dominated by more physical opponents, but he has put his injury problems behind him now and Chelsea's defence looked far more secure with him at the heart of it on Tuesday night.
Loic Remy's late goal ensured there was no clean sheet. But Lille did not threaten at all until that point and it had a lot to do with Rudiger.
He provided the leadership Chelsea's defence has lacked lately and looked assured from the start. The fans sounded their appreciation when he won an early foot race with Thiago Maia. There were roars of delight at one crunching tackle on Remy shortly before half-time.
Zouma clearly benefited from the presence of a more experienced centre-back partner alongside him, and while there was one late lapse from Rudiger - a loose touch which allowed Remy to spring forward on the break - this was an impressive overall performance for a player making his first start since September - and only his second of the entire season.
Either side of Rudiger and Zouma, Azpilicueta and Emerson fared similarly well, pinning back Lille's wide players for long periods, keeping their composure late in the game and even combining for what turned out to be the decisive goal, when the latter's corner was headed home by the former.
Jorginho ran the midfield. The Italy midfielder has been in and out of the Chelsea team lately, but he has been talked up as a "leader" by Lampard this season and this performance was another example of his value to the side. As well as the usual probing passes, he made more tackles and interceptions than anyone else, helping Chelsea keep Lille under pressure.
Jorginho was ably supported by N'Golo Kante and Mateo Kovacic, who combined to ensure Chelsea did not miss Mount's guile, and while it was Tammy Abraham who scored the opener, the striker was one of only two players in the team under the age of 25 along with Christian Pulisic.
Those two have been rightly praised this season, becoming talismanic figures in Lampard's side and scoring 19 goals between them in all competitions, but Willian is just as important to Chelsea's attack and that was evident again against Lille.
Nobody created more chances or had more shots than the Brazil international. While he turned 31 in August, the turn of pace which allowed him to pick out Abraham for the first goal was a reminder that he has lost none of his explosiveness. The pinpoint crossfield pass to set up a chance for Callum Hudson-Odoi in stoppage time was another individual highlight.
It is young players like Hudson-Odoi who have won Chelsea so many admirers this season, but it was the older heads who were needed on Tuesday night. Now facing a Champions League draw which will pit them against either Paris Saint-Germain, Bayern Munich, Juventus, Barcelona or RB Leipzig, Chelsea are sure to need them again in the knockout stages.