The finish was far from straightforward but Djebbour easily rounded Fabianski and converted from an acute angle.
A banner had been unveiled across one entire end of the atmospheric Georgios Karaiskakis stadium instructing the Olympiakos players to score, win and let us dream and, within 16 minutes, they obliged. .
The Spanish midfielder then tried to lift his shot over Mannone but actually succeeded only in sending what amounted to a tame back-pass towards the Arsenal goal. Djebbour threatened again moments later, only to collide with Fabianski who was stretchered off with a deep cut on his knee.
There was further defensive disruption when Santos was forced off. Squillaci and Djourou collectively failed to clear David Fusters through-ball and instead played Rafik Djebbour through on goal. He missed, and could only look over his shoulder at the agonising sight of the ball dribbling into an empty net.
With Arsenal now fielding four natural centre-backs, the team might have been expected to lack width but Ignasi Miquel then helped them back into game. Vito Mannone, his replacement, was soon picking the ball out of his own goal in embarrassing circumstances.
Mannone, though, suddenly seemed consumed by panic and inexplicably tried to volley the ball to safety from well inside his own area.
The goal briefly lifted Arsenal but their defensive deficiencies remained evident as Olympiakos added a deserved third when Modesto followed up after Olof Mellbergs header had bounced off the post.
Emmanuel Frimpong was caught in possession by Giannis Maniatis who played a hopeful through-ball that Mannone headed straight to Fuster. His curling cross was chested down by Chamakh and Yossi Benayoun struck a powerful volley past Balazs Megyeri