Arsenal lead Olympiakos, 2-1, at Emirates Stadium in an intense match, at halftime.
David Fuster scored to cut the lead in half for Olympiakos.
Arsenal received goals from Alex Olxade-Chamberlain and Santos within the first 20 minutes.
Gunners manager Arsene Wenger is sitting in the stands as he serves a suspension. Robin van Persie and Aaron Ramsey are on the bench. It is a makeshift squad for Arsenal. They are battling injuries, and Wenger decided to rest some key players.
Olympiakos has 11 shots, with five on goal, and showed much better poise and confidence after the two Arsenal goals. However, Arsenal have had possession for 64 percent of the match.
Tomas Rosicky earned a yellow card in the first half after a foul just outside the box.