Gervinho opened the scoring for Arsenal in the 42nd minute with a nice finish from the edge of the box.
Olympiacos equalised only 3 minutes later when Mitroglou headed home a cross from the left.
Arsenal retook the lead in the 56th minute after good work down the left from Gervinho and Podolski struck the ball home.
Aaron Ramsey applied the cheery on top of the victory with a cool finish over the top of the onrushing Olympiacos goalkeeper.
