Arsenal initially rode some early pressure from Lens and took the lead in the 14th minute when Gabriel Jesus capitalised on a through-ball from Bukayo Saka to find the back of the net. However, Saka was forced to leave the pitch with a heel injury just 33 minutes into the game, dealing a blow to the Gunners.
Lens didn't take long to respond, with Adrien Thomasson curling a superb finish into the far corner to level the score 11 minutes later. The home side continued to threaten Arsenal's defence, with Kevin Danso's shot narrowly missing the target and Thomasson's header coming close before being ruled offside.
The turning point came in the 69th minute when Elye Wahi, who had joined Lens from Montpellier in the summer, delivered a first-time finish into the bottom left corner from a Przemyslaw Frankowski cross. This goal secured a notable victory for Lens, marking their return to the Champions League stage in style.
Gabriel Jesus, who had earlier scored for Arsenal, continued his impressive form in the competition, as he has now been involved in 16 goals in his last 16 Champions League starts, tallying 13 goals and three assists.
The victory propelled Lens to the top of Group B with four points, while Mikel Arteta's Arsenal sit in second place with three points. Arsenal will now have to regroup quickly as they prepare for a crucial Premier League showdown against Manchester City on Sunday.