The Gunners have now lost their opening two group matches for the first time ever following their 2-1 defeat at Dinamo Zagreb two weeks ago and are bottom of Group F, six points behind leaders Bayern Munich, who they have to play twice.
Olympiakos, whose 12 previous visits to England since 1965 all ended in defeat, scored as many goals in this match as they had managed in the last 50 years in England, and have three points along with Dinamo, who were beaten 5-0 at Bayern.
The defeat left Arsenal manager Arsene Wenger in a tetchy mood when he faced the media at the post-match news conference.
