Rafa remains on course

Nadal: Simon next up

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An elusive US Open crown remains on the cards for top seed Rafael Nadal after he displayed all his renowned fighting spirit to defeat Denis Istomin.

The Flushing Meadows title is the last piece of the jig saw in the world number one's quest for the career Grand Slam, and the Spaniard was forced to battle his way into the third round on Arthur Ashe Stadium.

Nadal, who has yet to reach the final in New York and could meet Andy Murray in the semis, cruised through the opening set against the in-form Istomin - a finalist in New Haven last week - but found himself 5-1 down in a second-set tie-break.

The eight-time major champion dug deep to somehow win the next six points in a row - one of them with a lucky net cord - en route to a 6-2 7-6 7-5 victory in two hours and 44 minutes.

Nadal, who has already collected the French Open and Wimbledon titles this year, paid tribute to a gutsy performance from the world number 39, who deserved to take the match into a fourth set at least.

Lucky

"He was playing really well," Nadal said of Istomin. "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," added the 24-year-old left-hander.

"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."

Up next for Nadal is Frenchman Gilles Simon, who edged past 29th seed Philipp Kohlschreiber of Germany in five sets.

Querry, Nalbandian through

Meanwhile, American hopeful Sam Querrey joined compatriot John Isner - an earlier winner - in the third round after a straight-forward 6-2 6-3 6-4 to win over Marcel Granollers.

The 20th seed, who could face British hope Murray in the fourth round, set up a clash with Granollers' countryman and 14th seed Nicolas Almagro - who beat fellow Spaniard Guillermo Garcia-Lopez in four sets.

It was not all good news for the Americans on day five, as 18-year-old qualifier Ryan Harrison suffered a heartbreaking defeat, squandering three match points in a fifth-set tie-breaker before losing to Ukraine's Sergiy Stakhovsky 6-3 5-7 3-6 6-3 7-6.

David Nalbandian, the 31st seed, had little trouble booking his place in the third round after posting a 7-5 6-4 6-2 victory over Frenchman Florent Serra.

The Argentine star, who missed the previous six grand slams with hip and hamstring injuries, has been tipped as one of the outsiders for the title and will face eighth seed Fernando Verdasco for a place in the last 16.