Arsenal boss Arsene Wenger was delighted with the professionalism of their performance in victory over Olympiakos.
The Gunners won through late goals from Robin van Persie and Andrey Arshavin.
"We had a great first half, with outstanding quality, but unfortunately we could not take advantage," said Wenger. "Then you know it is difficult to maintain that pace and quality for 90 minutes.
"In the second half, we dropped a bit physically and our fluency went a bit as well. Then it is about not making a mistake, digging deep and hoping they die a bit more than us in the last 20 minutes and that is what happened.
"We dominated this team from the first to the last minute, but there were well organised and disciplined.
"They waited for us, are very strong on pieces. We were wobbling a bit on one or two and maybe they hope for that.
"But maybe because we did not allow them to come out, that they did not come out."
Wenger added: "We keep our composure and kept going.
"We played with a desire to keep the discipline in the team. We did not do anything crazy. I always felt we could score. We have matured and a game like this shows just that."
