Platt says City were well worth the three points against the champions-elect.
He told City TV: "More than a fantastic result it was a terrific performance.
"You are never going to dominate a game for 90 minutes against Manchester United but we restricted them to very few opportunities.
"The opportunities they did have were on the counter-attack, which you expect from a team like them, but we took the game to them, we had territorial advantage, we created opportunities.
"We were composed throughout, which was a good thing.
"But not only that, we showed character as well. Having conceded the goal to go 1-1 we showed the character to continue to go and finished it off with a great goal from Sergio."