The veteran striker came off the bench to settle a fiercely contested Ligue 1 encounter, rewarding Lille for their attacking pressure and ending Lens' three-match winning run in the league.
The result lifted Lille into second place in the standings, keeping them within reach of leaders Paris Saint-Germain.
Lille dominate but struggle to find breakthrough
Lille started brightly and created the clearer chances in the first half.
Ethan Mbappé came close with a curling effort that went narrowly wide, while Soriba Diaoune threatened with a close-range header that goalkeeper Robin Risser did well to save.
Diaoune was particularly unfortunate when another effort struck the crossbar following a corner, as Lille continued to press for the opening goal.
Lens also had opportunities to threaten, with Thorgan Hazard and Saud Abdulhamid testing goalkeeper Berke Özer. However, neither side could break the deadlock before the interval.
Both goalkeepers keep the score level
Lille resumed the second half with renewed intensity. Nabil Bentaleb quickly released Ethan Mbappé with a clever free-kick, but Risser produced another important save.
Lens almost punished the hosts on the counter-attack when Florian Thauvin found himself through on goal. Özer reacted well to deny the former France international and keep Lille in the contest.
Hakon Arnar Haraldsson also tested Risser from inside the penalty area, but the Lens goalkeeper continued to frustrate the home side.
Giroud delivers decisive moment
With the match approaching its conclusion, Lille introduced Giroud in search of a breakthrough.
The decisive moment arrived in the 87th minute. Bentaleb unleashed a powerful effort from distance, which Risser could only parry into the path of Giroud.
The experienced forward reacted quickly, controlling the rebound before firing home with his left foot to send the home supporters into celebration.
It was Giroud's second consecutive league match with a goal and a decisive contribution in one of French football's biggest regional rivalries.
Lille move into second as Lens suffer setback
The victory ended Lille's four-match winless run in all competitions and moved them into second place in Ligue 1, keeping the pressure on PSG at the top.
Lens, meanwhile, saw their three-game winning streak in the league come to an end and remained five points behind Lille.
Lille will now turn their attention to the UEFA Champions League, with a trip to Norway to face Bodø/Glimt scheduled for Tuesday before returning to domestic action against Rennes.
Match details
• Competition: Ligue 1, Matchday 9
• Result: Lille 1-0 Lens
• Venue: Decathlon Arena – Stade Pierre-Mauroy, Lille
• Date: Friday, 30 October 2026
• Goal: Olivier Giroud 87'
• Flashscore Man of the Match: Robin Risser (Lens)