Arsene Wenger was scathing of Arsenal’s performance as they launched their Champions League Group D campaign with a chastening 2-0 defeat at Borussia Dortmund.

Ciro Immobile and Pierre-Emerick Aubameyang struck either side of half-time but the German club would have won by a landslide if it were not for the reflexes of Wojciech Szczesny and their own wastefulness.

Arsenal’s defending was woeful and reached its nadir for Immobile’s opener, but Wenger admitted they had under-performed across the pitch.

“We lost the ball at the throw in but it was still three against Immobile at the back,” Wenger said.

“It’s still difficult to understand how we conceded the goal. There were still enough people to stop the goal.

“Dortmund were very strong in midfield. They were stronger than us in midfield.

“But it’s very difficult on the night to go into any individual assessment of any player because as a team we were not at the requested level.

“It was a difficult night. Dortmund were the better team. Our performance was disappointing.”

Three days after missing a guilt-edged chance against Manchester City’s Joe Hart, new signing Danny Welbeck failed to covert a one-on-one with another goalkeeper.

This time Roman Weidenfeller was the beneficiary of his wayward finishing and crucially the chance came four minutes before Immobile’s opener.

Welbeck’s record in front of goal has been criticised, but Wenger claimed his £16million deadline-day signing from Manchester United needs time to settle.

“The paradox of the night is that we had very good chances to score first, but they then scored from counter-attacks,” Wenger said.

“Danny will improve, I don’t think we have to make a problem of that.

“He had a very lively first-half. He had two or three good chances but couldn’t finish them. There was one obvious one. We have to be patient with him.”