Arsenal went top of Group B with a 2-1 win over Sevilla.
The Gunners came into the game with three points from two games, after beating PSV and losing 2-1 at Lens.
Gabriel Martinelli gave Mikel Arteta’s men the lead in the first half, rounding the goalkeeper to slot into an empty net.
Gabriel Jesus then curled in a spectacular effort, before Nemanja Gudelj pulled one back for the hosts.
At Old Trafford, Harry Maguire’s header proved to be crucial, as Manchester United saw off FC Copenhagen 1-0.
The Red Devils had Andre Onana to thank, as the Cameroon goalkeeper saved a last-minute penalty to ensure United won their first game of this season.
Real Madrid also thrashed Braga 2-1, with Jude Bellingham’s strike proving to be decisive.