By Tom Pilcher
NEW YORK (Reuters) - Holder Rafa Nadal and fourth seed Andy Murray will need to be razor sharp to win their U.S. Open quarter-final matches against big-serving 2003 champion Andy Roddick and fellow American blaster John Isner Friday.
All of Roddick's three victories against Nadal in their nine meetings have come on hard courts, including a second-round U.S. Open clash in 2004, with the Spaniard paying tribute to his last eight opponent's longevity.
"He's having one of the best careers, being in the top players for, I don't know, 11 years, 10 years, nine years. That's a lot. That's amazing. So I have big respect for Andy," 10-time grand slam winner Nadal told reporters Thursday.
Roddick knows he will have to reproduce the form he showed in the last 16 Thursday against fifth-seeded Spaniard David Ferrer on a jam-packed outside court.
"I'm gonna have to play pretty aggressively now, similar to what I did today. He's (Nadal's) one of the greatest ever, so I'm gonna have to have a repeat at least," the 21st seed said.
The towering Isner, renowned for beating Nicolas Mahut 70-68 in a fifth set epic at last year's Wimbledon in a match that lasted over 11 hours, will need to stock up on shirts for his semi-final against the super-fit Murray.
Murray won the only previous meeting between the pair, in straight sets at last year's Australian Open last 16 clash, but for all their lack of playing experience against each other Isner is a tricky opponent, according to the Briton.
"He's got a huge serve and can hit big forehands and is a little bit erratic and doesn't give you much rhythm," said the world number four, who produced fine form as he brushed aside American wildcard Donald Young Thursday.
Shirts aside, Isner needs his biggest weapon -- his booming serve -- to be firing on all cylinders to stand a chance.
"He's one of the best returners in the game, so I'm going to have to serve my best," he summed up matter-of-factly.
Isner and Murray are scheduled to play first on the vast Arthur Ashe stadium at 1200 local time (1600 GMT), to be followed by Nadal and Roddick.
(Editing by Mark Lamport-Stokes)