Arsenal manager Arsene Wenger has defended his decision to select David Ospina over Petr Cech in his side's 3-2 defeat to Olympiacos in the UEFA Champions League.

Wenger's decision to select the Colombian for the Group F clash backfired spectacularly as Ospina dropped the ball over the goal line from a corner to put Olympiacos 2-1 up.

Theo Walcott had cancelled out Felipe Pardo's opener and, while Alexis Sanchez levelled after the break, Alfred Finnbogason struck the winner just a minute after the Chilean's equaliser in an enthralling contest.

Having suggested a calf injury had kept Cech out pre-match, Wenger told BT Sport afterwards: "A goalkeeper can make a mistake but it doesn't explain why we lose.

"That can happen, it happened to Petr Cech already [this season], you have to accept that."

Wenger claimed that an inability to stay tight at the back after Sanchez's equaliser was to blame for his side's defeat - with back-to-back losses making hopes of progression appear gloomy with consecutive fixtures against Bayern Munich to come.

"[Qualification] is still possible but it's difficult to swallow losing a game like that," Wenger said. "It was a combination of a lack of defensive concentration, good defending from Olympiacos and also bad luck as well.

"They had four shots on goal and we conceded three, it's difficult to swallow. I felt it was a typical game where you dominate but you have to absolutely be focused and not make the task more difficult.

"At 2-2, we gave them another goal straight away and if we stay at 2-2 for five minutes more we win the game.

"It took a while to get into the game because we had a very intense game on Saturday but the second half was the turning point.

"We put effort in but everything went against us tonight."