Henrikh Mkhitaryan scored his first Arsenal goal as his new club rebounded from a run of four successive losses with a 2-0 win at AC Milan in the first leg of the Europa League last 16 on Thursday.
There was another surprise in Germany where two goals from Valon Berisha led Salzburg to a 2-1 victory at Borussia Dortmund.
Atletico Madrid recorded a comfortable 3-0 home win over Lokomotiv Moscow while CSKA Moscow was beaten 1-0 in Russia by Lyon.
A minute’s silence was observed at every match in honour of Davide Astori, the Italy and Fiorentina player who died last week at the age of 31.
In a tussle of two heavyweights with proud histories, Arsenal went ahead after 15 minutes when Mkhitaryan, signed from Manchester United in January, saw his right-foot shot deflect into the net off Milan captain Leonardo Bonucci.
Mkhitaryan also hit the crossbar towards the end of the first half.
Bonucci almost levelled for Milan two minutes before the interval when he rose in the penalty area to head a corner narrowly wide.
Mesut Ozil then laid on the second goal in first-half stoppage time for Aaron Ramsey, who went round goalkeeper Gianluigi Donnarumma to give his team a healthy advantage to take into the second leg next Thursday.
Saul Niguez fired a spectacular shot from 25 metres to put Atletico in front against Lokomotiv in the 22nd minute before Diego Costa added his sixth goal in 13 matches since rejoining the club from Chelsea.
Costa pounced to score after Antoine Griezmann’s goalbound effort was saved before captain Koke made it 3-0 in the final minute.
Atletico has reached two Champions League finals since winning the Europa League in 2012.
Berisha was twice on target early in the second half, his opener coming from the penalty spot, to put Salzburg on top before Andre Schurrle pulled a goal back for Dortmund.
Lyon was indebted to a 68th-minute header from Marcelo as the French team triumphed at CSKA.
There are four more games later on Thursday.