Paris - Danny Welbeck pounced on a defensive lapse to snatch a 1-0 victory for Arsenal at Sporting Lisbon in the Europa League on Thursday, while seven-time European champions AC Milan crashed to a home defeat by Real Betis.
England forward Welbeck struck a 78th-minute winner in Portugal as he punished a mistake by former Liverpool defender Sebastian Coates to hand Arsenal a third win in three matches in Group E.
Unai Emery's Gunners have now won 11 games in a row in all competitions - the club's best run since 2007 - and are on the verge of qualifying for the Europa League last 32.
Gennaro Gattuso's Milan dropped their first points in Group F as goals from Antonio Sanabria and Giovani Lo Celso, on loan from Paris Saint-Germain, earned Betis a famous 2-1 win in Italy.
Patrick Cutrone grabbed a consolation for Milan who finished the game with 10 men after Samuel Castillejo saw red for the hosts in injury time.
Olympiakos beat Dudelange of Luxembourg 2-0 in the group's other fixture, while there was more misery for Brendan Rodgers and Scottish champions Celtic in Germany.
Brazilian striker Matheus Cunha and Portugal winger Bruma, who scored against Scotland in a friendly this month, were both on target in the first half as RB Leipzig won 2-0.
Salzburg picked up a third successive victory to stay top of Group B as Munas Dabbur netted twice in a 3-0 defeat of bottom side Rosenborg.
Chelsea can take a large step towards the knockout phase when they host BATE Borisov of Belarus later, while Steven Gerrard's Rangers face Spartak Moscow in Glasgow.