Despite qualification and top spot already secure before Tuesday night's clash in Athens, Wenger - taking charge of his 200th European tie - expected better as defensive lapses from what was an experienced back four again proved costly as the visitors trailed 2-0 at the break. In-form Algeria striker Rafik Djebbour slotted home on 16 minutes after a loose ball was not cut out at the edge of the area, before substitute keeper Vito Mannone - on for the injured Lukasz Fabianski - made a hash of his clearance as David Fuster put the hosts in the driving seat to reach the last 16. Yossi Benayoun slotting home a consolation on 57 minutes before Francois Modesto secured victory with a minute left. However, that was not enough as rivals Marseille produced a late rally to win at Borussia Dortmund and deny the Athens club qualification as they had to make do with the Europa League instead. Wenger, who revealed full-back Andre Santos was set for a spell on the sidelines after going off with an ankle injury, felt the fact Arsenal had nothing to play for proved a telling factor. "We had the early chances, but Olympiacos played a very committed game and made a good battle," said Wenger. "We lost too many balls in the first half and overall became a bit insecure. "They were sharper than we were at 2-0, but we came back and then looked like we could equalise, but they scored the third goal. Overall Olympiacos deserved to win. "Unfortunately for them it is not enough to qualify as Marseille made a super result in Dortmund." Wenger added: "I am annoyed because we lost the game, it is difficult to single [anyone] out. Offensively and defensively we were not convincing. "We could sense there was something more at stake for Olympiacos than us, and that made a difference." While the extent of Santos' injury is not yet clear, Wenger said the Brazilian would be "out for a while", and also confirmed reserve keeper Fabianski had suffered a "deep cut on the knee". Despite the disappointment of the defeat, Wenger feels the trip to Greece and the intimidating Georgios Karaiskakis Stadium will have stood the likes of Emmanuel Frimpong, Francois Coquelin and England Under-21 international Alex Oxlade-Chamberlain in good stead. "It was a fantastic experience they realise what intensity that you need at this level and some young players have shown good things," said Wenger. "But there was a bit of lack of experience and maturity in midfield where you need to hold the ball better when we were under pressure." For Olympiacos coach Ernesto Valverde, it was a case of so near yet so far as his men just could not overcome a home defeat to Marseille on Matchday One, which came when they had not played a domestic game because of the Greek match-fixing scandal which saw their schedule rearranged. "We have to be proud. We played a great game against Arsenal, who came here to give us nothing," he said. "It was cruel the way we have been left out of the next phase because in the last five minutes we thought Dortmund were winning the game. "We can't talk about justice in football, just success at the right time. The good thing is we fought until the very last moment." Valverde added: "The game against Marseille really cost us. We had not played a competitive game for four or five months, but this is football. "If football games lasted 85 minutes we would be in the next phase, but they last 90 minutes."