PIRAEUS, Greece (AP) -- Substitute Costas Mitroglou fired Olympiakos to a 2-1 victory over Arsenal in the Champions League on Tuesday, as the Greek champions came from behind with two goals in nine minutes.
The London side took the lead against the flow of play in the 38th minute with Tomas Rosicky, set up by Gervinho, who switched to the right, outran two defenders and skillfully swung the ball back.
Olympiakos dropped back despite having the early initiative, helped by Algerian duo Djamel Abdoun and Rafik Djebbour, who missed some early chances.
Arsenal captain Thomas Vermaelen stopped successive attacks in central defense before the visitors were eventually overrun at Piraeus' Karaiskaki Stadium near Athens.
But Yiannis Maniatis leveled in the 64th, pouncing on a defensive error when Aaron Ramsey foolishly chested the ball down.
Mitroglou scored the winner in the 73rd, powering the ball past Arsenal goalkeeper Wojciech Szczesny from outside the area, just a minute after coming on.
"We had a good first half, but I believe we dropped physically in the second half because many of the players didn't have the match experience at that level," Arsenal manager Arsene Wenger said.
His whose team had already qualified from Group B, while Wenger marked his 150th Champions League match.
He traveled to Greece without several key players, including Theo Walcott and Lukas Podolski, before the match against West Bromwich Albion in the Premier League on Saturday.
"It is positive tonight because we left eight or nine players at home," Wenger said.
The French manager appeared irritated with Spanish referee Alberto Mallenco, who awarded Olympiakos a corner that led to the Greeks' first goal after ruling that Szczesny had touched the ball.
"It was a very, very bad decision against us," Wenger said. "I don't like to say anything about the referee, but I would like at least for them to concentrate on the job ... I don't want to make too much fuss about it so we have to take it on the chin."
Wenger said he replaced Rosicky at halftime with Andrey Arshavin as a precaution, with the Czech veteran having recently returned from a six-month injury absence.
The Greeks were already destined for the Europa League.
"It's fair to say we are not happy because we were already out of the Champions League. But we wanted a win tonight and to make the fans happy -- and we did that," Olympiakos coach Leonardo Jardim said.
"It's true that our league starts late and that cost us in the early games ... every coach and every player wants to be in the Champions League. Now we must focus on the Europa League."
Olympiakos' standout defender Costas Manolas shared the frustration.
"It was a great night for us. It's a shame we were out of the Champions League, the way we played. We fought hard and came from behind," Manolas said.