Top seed Rafael Nadal displayed all his renowned fighting spirit to beat Denis Istomin and complete the third round line-up at the US Open.

Nadal cruised through the opening set against the in-form Istomin - who reached the final in New Haven last week - on Arthur Ashe Stadium, but found himself 5-1 down in a second-set tie-break.

But the world number one dug deep to somehow win the next six points in a row - one of them with a lucky net cord - on his way to a 6-2 7-6 (7/5) 7-5 victory in two hours and 44 minutes.

Nadal, who needs to lift the title on September 12 to complete the career Grand Slam, paid tribute to a gutsy performance from Istomin, the world number 39 deserving to at least take the match into a fourth set.

"He was playing really well," Nadal admitted. "He had a great tournament last week and so he was playing with confidence today and I was a little lucky in the tie-break.

"I started the match well, my serve keeps working well but every match is really difficult."

One of Nadal's serves was clocked at 134mph, well down on the likes of Andy Roddick perhaps, but certainly one of the fastest the Spaniard has ever produced.

"I am working on my serve all my life, sometimes it works well, sometimes it's not working all that well," Nadal added. "A few days ago I started to feel very well with my serve and the first two matches I have not lost my serve which is very good for the confidence."