US Open photos

Sixth seed Lleyton Hewitt reached the fourth round of the US Open when Czech Radek Stepanek retired due to back pain.

The Australian won nine of the first 10 games and was leading 6-1 3-0 when Stepanek called a trainer to the court.

Gamewatch: Hewitt v Stepanek

The 24-year-old Czech lay on his stomach while the trainer rubbed his lower back. He lost two of the next three points and then quit the match.

It was the second time this year Hewitt has ousted Stepanek from a Slam, having knocked him out of the Australian Open in the third round as well.

Hewitt, the 2001 US Open and 2002 Wimbledon champion will face 11th seed Paradorn Srichaphan of Thailand on Monday for a quarter-final berth in the year's final Grand Slam event.

Srichaphan equalled his best showing at a Grand Slam tournament by defeating Spanish lucky loser Fernando Verdasco 6-3 6-4 6-3.

The Thai player also reached the fourth round of Wimbledon this year where he was beaten by American Andy Roddick.

American Taylor Dent had an impressive win over 15th seed Fernando Gonzalez of Chile.

Dent proved a resilient opponent in an epic encounter, which he won 7-6 6-7 3-6 7-6 6-4.

Fifth seed Guillermo Coria of Argentina enjoyed a 7-5 6-1 7-5 victory over France's Gregory Carraz.

Coria will face Jonas Bjorkman for a berth in the quarter-finals after the Swede ousted Slovakia's Karol Kucera in a five-set thriller ) 6-4 4-6 6-7 6-4 6-4.

Former finalist Todd Martin is also into round four after coming back from a set down against compatriot Robby Ginepri to win 6-7 7-6 6-4 6-4.

Martin will face French Open champion Juan Carlos Ferrero of Spain who advanced to the fourth round by spoiling the 24th birthday of Argentina's Juan Ignacio Chela, with a 7-5 7-5 6-1 win.

Andre Agassi's match with Yevgeny Kafelnikov will finish on Sunday after rain halted their third-round clash.

Agassi took the first set 6-3, but the eight-time Grand Slam champion was broken in the first game of the second set before showers stopped play.