Sergio Aguero's brace and further strikes from Yaya Toure and Samir Nasri earned City a win which reflected their dominant performance.
The game rekindled memories of their 6-1 away win over United in their Premier League title-winning campaign two years ago, but Kompany dismissed suggestions they had made a "statement" in the title race.
"I think you make a statement over the whole season," he said. "It's too early to say it's a defining game.
"When we won 6-1 at Old Trafford I said we needed to stay humble, it's only three points.
"But it gives us all the confidence and allows fans to celebrate for a couple of days."
Asked about why his side were so dominant, Kompany told Sky Sports 1: "Maybe the game meant a little bit more to us than to them.
"We've been looking forward to it, our fans have been speaking about it for a long time and we needed to win.
"We have a fantastic home record and we know there is no reason we should fear the opposition."