Big-serving John Isner stunned fifth-seeded fellow American Andy Roddick 7-6(2) 6-3 3-6 5-7 7-6(5) on Saturday to advance to the fourth round of the U.S. Open.

The 2.06-meter Isner produced 38 aces in the thrilling five-set victory over the 2003 winner and this year's Wimbledon runner-up.

Roddick, who served 20 aces himself, saved two match point from 3-6 in the tiebreak with a pair of aces before he netted a forehand return to end the three-hour 51 minute battle.

The 55th-ranked Isner, who had lost his two previous career matches against Roddick, will next meet 10th-seeded Fernando Verdasco of Spain, who survived a battle of his own before eventually overcoming 20th seed Tommy Haas 3-6 7-5 7-6(8) 1-6 6-4.

Five-times champion Roger Federer lost his first set of the 2009 U.S. Open but rallied to defeat former winner Lleyton Hewitt 4-6 6-3 7-5 6-4 and reach the fourth round at Flushing Meadows.

Hewitt, a former world number one and 2001 Open champion, lost to Federer for a 14th successive time.

The 28-year-old Federer, who is seeking his 16th Grand Slam title, will next face Spanish 14th seed Tommy Robredo, who beat American 21st seed James Blake 7-6(2) 6-4 6-4.

Novak Djokovic survived an unlikely battle with American world number 276 Jesse Witten before clinching a 6-7(2) 6-3 7-6(2) 6-4 victory in the third round.

The fouth-seeded Serb will play for a quarterfinal spot against Czech 15th seed Radek Stepanek, who bounced back from dropping the first set to beat Philipp Kohlschreiber 4-6 6-2 6-3 6-3.

Nikolay Davydenko did just enough to come through a straightforward match with Switzerland's Marco Chiudinelli, winning 6-4 7-5 7-5.

Though the world number 161 matched the eighth seed for much of the match, Davydenko got crucial service breaks right at the end of all three sets to earn a fourth-round match with Robin Soderling.

Soderling came through a back-and-forth match with American Sam Querrey 6-2 7-5 6-7(6) 6-1.

(Xinhua News Agency September 6, 2009)