Arsenal missed out on the chance to top their Champions League group after they conceded twice in 10 minutes to lose against Olympiacos.
The Gunners had the lead at the interval thanks to a strike from Tomas Rosicky but collapsed after the break to make it four games without a win in all competitions.
A much-changed Gunners side featuring Marouane Chamakh and Jernade Meade made a bright start in the early stages.
Aaron Ramsey spurned Arsenal's best opening with 15 minutes gone, failing to control from close range after a headed pass from Chamakh.
Olympiacos began to control possession as the half wore on and threatened through Djamel Abdoun, who fizzed a cross into a dangerous area before Arsenal cleared their lines.
Arsene Wenger's side grew in confidence and took the lead five minutes before half time through Rosicky, who curled home from close range after fine work from Gervinho to create the opportunity.
The home side started the second half with intent and purpose and equalised from a contentious corner.
A delivery from Abdoun came off Ramsey's chest and fell to Giannis Maniatis, who made no mistake from close range.
Olympiacos were ahead shortly after through Kostas Mitroglou, who placed a curling strike into the far corner just minutes after coming on as a substitute.
Wenger's men were unable to provide a response but are still safely through to the Champions League knockout stages.