Rafael Nadal powered past Chung Hyeon into the US Open fourth round, capitalising on the extra rest he enjoyed before facing the South Korean.

The Spanish second seed, who had a walkover in the previous round, had not played since Tuesday and it showed in a dominant 6-3 6-4 6-2 win.

By contrast, Chung had come through three rounds of qualifying and spent nine hours more on court.

Nadal faces 14th seed John Isner or 2014 champion Marin Cilic next.

'Merciless' Nadal marches on

With defending champion Novak Djokovic and 20-time Grand Slam champion Roger Federer in the opposite side of the draw, Nadal has - on paper at least - a more favourable route to a potential fifth US Open final.

Any concerns over the Spaniard's fitness after he withdrew from this month's Cincinnati Masters because of fatigue have been dispelled here with two ruthless displays in his two matches.

The 18-time Grand Slam champion did not face a single break point against Chung, who was a top-20 player and Australian Open semi-finalist last year.

He sealed the first set with an ace, the second when he forced the South Korean to hit long and then took victory on his first match point with a rasping forehand winner.

"Nadal is merciless," former player Jeff Tarango said in BBC Radio 5 Live commentary. "I don't think I've ever seen a human being, animal, or any kind of species, more competitive than Rafa Nadal. Ever. The dude is always competing. He always has to be playing something or winning at something. He never stops."

Last year Nadal reached the semi-finals here but was forced retire at the end of the second set against Juan Martin del Potro because of a knee injury.

On his way there he had come through two four-setters and a five-setter, which he says took their toll, and so the fact he has reached the second week at Flushing Meadows by spending little more than four hours on court could help him.

Against Chung, he had dispensed with the tape he usually has strapped around his knees.

"The tape is not working any more," he told the Arthur Ashe Stadium crowd. "But I'm happy to be playing on the hard court. I'm trying to play a bit more aggressive. I'm happy to be in the fourth round one more time."