By Steve Keating

NEW YORK (Reuters) - Fourth seed Rafa Nadal showed he is healthy and ready to challenge for a third U.S. Open title as he rolled into the last 16 at Flushing Meadows on Friday with a fist-pumping 6-1 6-4 6-2 win over Russian Andrey Kuznetsov.

Erasing any lingering concerns over an injured left wrist that kept him out of Wimbledon, Nadal has made a powerful start to the year's final grand slam, racing into the fourth round without dropping a set.

It was vintage Nadal on a warm New York evening, as the energetic Spaniard wore down his 47th-ranked opponent with a breathless work rate and a bombardment of stinging forehands.

"I am improving with that shot," Nadal told reporters. "Everybody knows that is a very important shot for me.

"When I am able to play that shot well, then the court opens a lot."

Nadal, who incurred his wrist injury at the French Open and then missed Wimbledon, showed his form when he reached the semi-finals of the singles and won the doubles gold medal at the Rio Olympics last month.

Two weeks later, saying he felt fatigued, Nadal lost his second match at Cincinnati but has certainly appeared re-energized since arriving at Flushing Meadows.

The 14-time grand slam winner concedes he still feels some discomfort in his wrist but it has not affected his performance on the New York hardcourts.

"Still (feel) something but something that is not limiting my game now," said Nadal. "That's the most important thing.

"I don't know in which kind of level I am.

"Is true that when I had to stop I was playing great. I felt myself ready for the French.

"For me is a great news that I am on the tour again and I am playing every day with less pain on the wrist."

Despite the one-sided scoreline, Nadal did his best to keep another large crowd at Arthur Ashe Stadium entertained on Friday closing out the match in theatrical style, setting up the winning point with a between-the-legs lob that had fans on their feet.

The 30-year-old had them roaring again seconds later as he danced across the court in a succession of fist-pumps.

"Every victory helps for the confidence, especially when you feel that you played well," smiled Nadal, who will next meet 24th-seeded Frenchman Lucas Pouille, a five-set winner over Spain's Roberto Bautista Agut.

"I feel that today I played great tennis for a long time, for a lot of moments on the match."

(Editing by Andrew Both)