The 31-year-old Spaniard beat South Africa’s Kevin Anderson 6-3 6-3 6-4 to win his third title in New York.
Following his French Open success in June, it is the first time since 2013 that Nadal has won two Slams in a year.
“I wake up every morning with the passion to go on court and to try to improve things,” he said.
“I still want to compete and still feel the nerves every time that I go on court. While that keeps happening, I will be here.
“When some day arrives that I don’t feel the nerves or that extra passion for the game that I feel, it will be the day to say, ‘OK, I do another thing.’
“I am 31, I’m not 25, but I still have the passion and the love for the game.”
Nadal’s victory took him three away from Roger Federer’s all-time record of 19 Grand Slam titles, and the pair shared all four major victories between them in 2017.
That came after both men ended their 2016 seasons early through injury, casting doubts on their ability to even challenge for the biggest titles again.
“I just can say thanks to life for that opportunity,” said Nadal.
“Probably that’s why I still have chances to compete in this sport and to do it well. That’s all.”
Grand Slams: Rafa v Roger
Had Nadal converted his lead over Federer, 36, in the final set of this year’s Australian Open final in January, there would be just one major title between the pair.
“I really never thought much about that,” said the Spaniard. “I just do my way. He does his way. Let’s see when we finish.
“Three is a big difference. I really don’t think much about these kind of things.
“I’m very happy with all the things that are happening to me, to win this title again. I have this trophy with me.”
Coaching changes in Nadal camp
The US Open was the last Grand Slam tournament in which Nadal was accompanied by his uncle Toni, the man who first put a racquet in his hand when was three years old.
Former world number one Carlos Moya, a close friend of Nadal, will take on coaching duties alongside long-time team member Francis Roig from next year.
Toni Nadal will take on the running of his nephew’s tennis academy in Majorca, which opened last year, although the world number one did not completely rule out a return to the player box for his uncle.
“He’s going to stop and going to put more attention on the academy. That would be great for my academy, and will be great for the kids,” said Nadal.
“That doesn’t mean that Toni will not travel any more. No, no, I believe that it will be stupid to say that.
“But of course he will not be in the diary of my practices and of my travels.”