A knee injury forced Nadal to miss the last grand slam of 2012, spoiling his chances of reaching the final for a third straight year.
With Nadal absent, Britain's Andy Murray went on to win his maiden grand slam title, beating Novak Djokovic in a five-set thriller.
"When I was in that period of time outside of the tour I didn't follow the tour every week, because at the end I was focused on my recovery," Nadal told reporters at Flushing Meadows ahead of Monday's opening play.
"But a few matches you cannot miss, and for sure I watched all the final. It was a great final."
This time Nadal is back, fully fit and at the top of his game, having won back-to-back Masters events at Montreal and Cincinnati.
Nadal also missed this year's Australian Open but has been in great form since making his comeback, winning a record eighth French Open in June.
Because of his knee problems, Nadal has had to adjust his game for the North American hardcourt season, playing more aggressively to reduce the pounding on his legs, and he seems to have found the perfect balance.
"I think you can play aggressive when you are playing well. That's the first and important thing," the left-hander said.
"It's true I'm trying to take the ball a little bit early and that I worked on my game to be a little bit more aggressive.
"But at the same time, it's true that in the past when I was playing well on this surface I had good success too, so it's not something crazy that changed today."
Nadal's absence from last year's U.S. Open could have another positive effect, helping him regain the number one ranking from Djokovic because he has no points to defend.
Nadal, currently ranked second, can overtake the Serbian if he wins the U.S. Open and Djokovic fails to reach the final.
"This tournament will make the difference. It's true that I am having a great season. I am in a positive position," said Nadal, who has won nine titles in 2013.
"I'm gonna try...but being number one is not my goal. My goal is be healthy, have the chance to be competitive, and finish the year with a good feeling and having the chance to play well.
"If I am number one, it will be amazing, amazing season for me."
(Reporting by Julian Linden; editing by Gene Cherry)
