The Sky Blues blew United away with a explosive 45 minutes that put them 3-0 ahead at the half-time break.
"I felt on the pitch we could have done even better - converting our chances better, maybe put a little bit more on top of that," the Germany international said.
"But it was great, I don't want to complain about our first half performance, it was a joy to watch.
"That was important for the first leg, because it feels great to go home for the second leg with this result.
"It's a great score for us, but it's Man United so it's not done yet. If we play similar, then I don't think they will have any chance."