Rafa's news drop-shot

Defending champion Rafael Nadal shocked the US Open on Sunday when he collapsed with cramps during a bizarre news conference, while Andy Murray stayed on course for a semifinal clash against the Spaniard.

Nadal, 25, was talking to journalists two hours after his third-round win over close friend David Nalbandian, when he grimaced in pain, screwed up his eyes and slumped in the back of his chair, feeling his right leg.

The world No 2, a winner of 10 grand slam titles, slipped to the floor behind the table, and out of view of the media, while tournament medical staff were summoned.

The conference room lights were switched off before the top of Nadal's right leg was suddenly silhouetted above the desk as the physios got to work.

After 15 minutes of treatment, Nadal was back on his feet, insisting that the problem was merely cramping.

A smiling Nadal said the incident will not affect his preparations for his fourth-round match against Luxembourg's Gilles Muller, scheduled for tonight.

During his 7-6 (5), 6-1, 7-5 win over Nalbandian, played out over two hours and 39 minutes in the 29C heat, Nadal also needed treatment on his blistered right foot.

Muller, who reached the last 16 by beating Russia's Igor Kunitsyn 6-1, 6-4, 6-4, famously defeated Nadal at Wimbledon in 2005 before the Spaniard got his All England Club revenge this year.

British fourth seed Andy Murray, the 2008 runner-up, took his career record against Spanish left-hander Feliciano Lopez to six wins in six meetings thanks to an impressive 6-1, 6-4, 6-2 victory.

He now faces American wild card Donald Young, who reached the fourth round at a grand slam for the first time with a 7-5, 6-4, 6-3 win over Argentine 24th seed Juan Ignacio Chela.

Janko Tipsarevic steamed into the last eight last night, where a clash with celebrated fellow Serbian Novak Djokovic could await.

Tipsarevic, 27, reached the quarterfinals of a grand slam for the first time, prevailing in a baseline battle against former world No1 Juan Carlos Ferrero 7-5 6-7(7) 6-5 6-2.

Twenty aces made the difference for Tipsarevic, the last coming on his first match point against the 31-year-old Spaniard who has been slowed by a litany of injuries and dropped to 105 in the world.

Three-time champion Serena Williams, battling the wind as much as her opponent, eased into the quarterfinals with a 6-3 6-4 win over Serbia's Ana Ivanovic. Both players struggled with their serves and ground strokes in a gusty Arthur Ashe stadium but it was the American who fared better.

Williams, the 28th seed, will face Russia's Anastasia Pavlyuchenkova for a place in the semifinals.

Pavlyuchenkova beat seventh-seeded Francesca Schiavone in three sets yesterday. The 17th-seeded Russian won 5-7 6-3 6-4 in two hours, 41 minutes, as the youngest player left in the draw defeated the oldest.