United faced the Canaries just three days before the second leg of their Champions League tie against Real Madrid.
The 27-year-old told MUTV: "It was a massive game for us, we wanted to extend the lead at the top of the league.
"I'm sure you can see by the team the manager picked, he put a lot of experienced players out and made us aware that the Norwich match was more important than the game on Tuesday [against Real Madrid]. So, it was a good professional job and a well-deserved win.
"Early on in the season we were conceding too many goals. We seemed to have coped with that, we're not conceding and we're scoring goals so we're in a great position at the minute. So, hopefully we can continue for Tuesday."
The England striker added the fourth goal for the league leaders following a hat-trick from Shinji Kagawa.