City won 3-0 against Sunderland in their best performance of the season.
O'Neill revealed: "Perhaps the first goal upset our gameplan but we were beaten by a superior side.
"They were electric. They are fine players, champions of this country and playing big Champions League games.
"It was always the possibility if they got the second goal, they would cause havoc and that happened. If another 10 minutes went by they might get a bit nervy.
"You just have to take it, wait for international players to come back and then prepare ourselves for Newcastle.
"They deserved to beat us because they were much, much better than us.
"But that doesn't mean I'm not disappointed because we should have done better."