Arsenal are ahead against Olympiacos at the break thanks to a strike from returning playmaker Tomas Rosicky.
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.
Olympaicos began to control possession as the half wore on but were unable to force Wojciech Szczesny into making a significant save.
Djamel Abdoun threatened before the interval, using his pace and trickery to fizz a cross into a dangerous area before Arsenal cleared their lines.
Arsenal 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.
Arsene Wenger's side have already qualified but need to win the match to have any chance of topping their Champions League group.
Liam Power
