The forward's two goals took his tally to a club record-breaking 10 against Manchester City but it needed Robin van Persie's stoppage-time free kick to claim a key victory
Having lost at home and away in the league to their rivals last season, the England man's two goals put the Red Devils in front before Robin van Persie put down a City comeback with his stoppage-time free kick.
"It's fantastic. It's great for us to go six points clear against our closest rivals, especially after what happened last year. We've waited a long time for this to happen," Rooney told Sky Sports after the game.
The forward's double took him to 151 Premier League goals and a record-breaking 10 in Manchester derbies.
"Of course, it's great to score here but it doesn't matter whether it's against City or not," he insisted. "I'm scoring for Manchester United and enjoying it.
"Obviously it's a great day for us to win here. They've had a great home record and to spoil that is a great feeling.
"[The game was] crazy," Rooney added. "It's been like that all season for us.
"To lose a two-goal lead ... to be fair, we were hanging on a bit at the end. They had a couple of chances and a bit of magic got us the three points."
Van Persie's late strike capped a fine performance in his first Manchester derby but the Dutchman remarked of his goal: "Anything will do – just to win. We had a good start because of Wayne, two really good, clinical finishes, good attacks and then we went into control, which was good.
"City always come back and we knew that so it's a really special way to end this game, to get the three points in a dramatic way.
"Wazza asked me [before the free kick], he said: 'What are you gonna do? Are you gonna shoot or are you gonna cross it?' I said: 'I think I'll have a shot'."
There was controversy at the end of the game as Rio Ferdinand was hit by a coin thrown from the home crowd and Van Persie opined: "In general it was a great atmosphere, everyone was supporting their team.
"I missed the thing with Rio so I'll have to look back at it but that shouldn't really happen on a football pitch."