Martin Odegaard scored his first goal for Arsenal and Gabriel and Mohamed Elneny were also on target to give the English side a 3-1 win at Olympiakos in the first leg of their Europa League round of 16 tie on Thursday.
Odegaard, who joined Arsenal on loan from Real Madrid in January, fired the visitors ahead with a 34th-minute strike from 25 metres before Youssef El Arabi equalised for the Greek team in the 58th minute.