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, BBC reported.
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."
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."