Arsenal's Per Mertesacker reacts after their Champions League soccer match against Anderlecht at the Emirates stadium in London November 4, 2014. [Photo/Agencies]

LONDON - Arsenal manager Arsene Wenger slammed his side's defending after watching Anderlecht claw their way back from three goals down to earn a 3-3 draw in Champions League Group D on Tuesday.

The hosts were 3-0 ahead inside the hour and apparently cruising into the last 16 of the competition for a 15th successive season under the Frenchman when the wheels came off in spectacular fashion at The Emirates.

Instead of shutting up shop, Wenger's side capitulated in worrying fashion, allowing the Belgian champions to hit back with two goals from Anthony Vanden Borre, the second a penalty conceded by Nacho Monreal, before Aleksandar Mitrovic's 90th minute header left the home crowd stunned.

"Annoyed? Yes. But you have to give them credit. They did fight until the end and we gave a poor defensive performance from the first to the last today. We never felt comfortable," a rather nonplussed Wenger told reporters.

"We got punished. A bit of bad luck because the first goal was offside but our defensive performance was not good enough."

Even before Mikel Arteta gave the hosts a 25th minute lead from the penalty spot, Anderlecht had caused several anxious moments with their quick, incisive football.

However, when Arsenal's standout performer Alexis Sanchez smacked in a second and Alex Oxlade-Chamberlain made it 3-0 in the 58th minute, the home side's clear defensive frailties appeared a mere blemish to a decent night's work.

Vanden Borre was apparently offside when he pulled a goal back from close range but what happened after that left Wenger angry and perplexed.

"At 3-0 we thought the job was done. It was fatigue as well, they finished stronger and sharper. We got punished. It's very disappointing," he said.

"In the Champions League you need to be at the right mental level or you get punished. Certainly we were not. What I say in the dressing room stays in the dressing room."