Arsene Wenger has blamed last night's 2-1 defeat to Borussia Dortmund on a lack of maturity from his Arsenal team.

The Gunners suffered their first defeat since the opening day of the Premier League season as Robert Lewandowski scored on the break in the final 10 minutes to leave Group F in the Champions League in the balance.

Prior to the winner, Arsenal looked favourites to score the winner as Aaron Ramsey scored a disallowed goal and Santi Cazorla saw his effort cannon off the cross bar.

Speaking to reporters after the game, Wenger said the performance from his Arsenal players lacked maturity and the second goal was of particular annoyance.

He said: "If you cannot win the game, you don’t lose it.

"Especially in the second half when we were on top, we made things difficult for ourselves by giving them the second goal.

"We put ourselves on the back foot with the first goal and (we were) naive for the second goal.

"If you look at the number of saves our keeper had to make and you concede two goals, you can say that we can only look at ourselves for not being mature enough in situations like that."

The loss leaves Arsenal top of the group but on equal points with Napoli and Borussia Dortmund.

In the second round of fixtures Arsenal face Napoli and Dortmund away from home and face an up-hill battle to qualify.

Wenger, although admitting qualifying will be tough, remains confident.

"It is tight and difficult for us, but possible," he said.

"We need a result away from home, but we can do that."

UEFA Champions League
Borussia Dortmund