In a surprising upset, AS Monaco defeated ten-man Barcelona 2-1 in their Champions League opener after Barcelona's Eric Garcia received a red card in the 11th minute. Monaco took an early lead with a goal from Maghnes Akliouche, but Barcelona's Lamine Yamal equalized shortly after. However, George Ilenikhena scored the winning goal for Monaco in the 71st minute, sealing their victory and ending Barcelona's perfect start to the season. Arsenal, on the other hand, managed a goalless draw against Atalanta, with goalkeeper David Raya making a crucial penalty save. Notably, Yamal's goal made him the second-youngest scorer in Champions League history. The day's matches also featured Bayer Leverkusen's dominant 4-0 victory over Feyenoord and Brest's historic 2-1 win over Sturm Graz.