Rafael Nadal cherishes a year of being fully fit after setting up US Open final showdown with Kevin Anderson

The world No 1 came from a set down to beat Juan Martin del Potro in their semi-final clash in New York.

World No 1 Rafael Nadal celebrates reaching the US Open final. Mike Segar / Reuters

World No 1 Rafael Nadal, nagged for years by knee injuries but enjoying a stellar season, already has a prize more treasured than another grand slam title - a healthy campaign chasing them.

The 31-year-old Spaniard, who ousted Juan Martin del Potro on Friday to reach Sunday's US Open final and a showdown with South African Kevin Anderson, said the year he has enjoyed has brought a happiness no major crown can match after past seasons of misery unable to unleash his best efforts.

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"For me, more than winning grand slams or not - of course, if I win, I will be more happy - but is about being healthy and feeling well and competitive," Nadal said.

"That's already happened in the whole season. So that's the most important thing for me."

Nadal seeks his third US Open title after 2010 and 2013 and his 16th career major when he faces 28th seed Anderson.

"What is more important, more than winning Slams, is to be happy," Nadal said. "I am happy if I am healthy and happy if I feel competitive most of the weeks I'm playing and that's what happened this year.

"I am very happy to win Monte Carlo, Barcelona, Madrid and Roland Garros. I am very happy to be in the final here in the US Open ... and I am going to fight to win another title here. But still, a great season for me."

Nadal, who lost to Roger Federer in the Australian Open final but won his 10th French Open crown in June, has reached three grand slam finals for the first season since 2011.

He has not won multiple slams in a season since 2013, but he did thump del Potro for his 15th consecutive Slam semi-final triumph, the last loss coming to del Potro in the South American's 2009 US Open championship run.

"Important day for me. Important victory against a great opponent," Nadal said.

"I woke up today and said to myself, 'Today is the day that I'll play. I need to play with the right energy, and I need to increase the level of my game.'

"A lot of times I know that and it didn't happen, but today it happened."

Nadal said that sometimes the only way to get better is to win matches, victories building the final 20 to 30 per cent he needs to maximise his potent game.

"You need to win matches," Nadal said. "If you practice well and you feel yourself well, you have more chances to win matches in the tournaments.

"But this 20, 30 per cent, that's a big difference. You only make this winning matches, because it's about confidence. It's about things that when you are on court comes automatic.

"You don't have to think about what you doing in some important moments. Things comes straightaway without thinking that much and all these things happen only when you are in a good moment."

Few were better than his clay court run with two Spain titles, Monte Carlo and the icing on the cake coming at Roland Garros.

"Clay court season was unbelievable, so that helps a lot for my confidence, to be more calm and I'm here in the final," Nadal said.

"It's a great result for me already. I will now face a very tough opponent, probably the most important match for me that remains this year, so I gonna try my best to play my best."