New York ? They pushed their beleaguered bodies this way and that for 4 hours, 44 minutes on Friday, swatting balls from impossible angles and somehow rarely missing the mark.

Through repeated visits from trainers, through all manner of momentum shifts, No. 3-seeded Novak Djokovic and former top-10 player Radek Stepanek produced as entertaining and lengthy a U.S. Open match as there’s been in quite some time.

Djokovic has emerged as a potential challenger to No. 1 Roger Federer and No. 2 Rafael Nadal, and on this day, he emerged victorious, if only barely, beating friend and sometime-doubles-partner Stepanek 6-7 (4), 7-6 (5), 5-7, 7-5, 7-6 (2).

When it ended, Stepanek stepped over the net, dropped his racket and trudged over to apply a bearhug so hearty the weary Djokovic nearly toppled over.

“As much as I was running and sliding and cramping, whatever, I still had a lot of fun,” Djokovic said. “There are a couple of points that are really unforgettable.”

And, oh, how many points there were – 356 in all. The match lasted 63 games, the most at the U.S. Open since 1979. That year, John Lloyd and Paul McNamee played the same number to set the tournament record for most games in a singles match since tiebreakers were introduced in 1970.

“Long day,” Djokovic said. “Long match.”

It was another super day for his Serbia at another Grand Slam, too, with No. 3 Jelena Jankovic and No. 5 Ana Ivanovic reaching the women’s fourth round. Another Serb, Janko Tipsarevic, though, stopped because of an injury while losing 6-2, 6-3, 3-2 against Nadal. The Spaniard’s bothersome knees looked much better in the second round than the first, and he now meets Jo-Wilfried Tsonga, who ended six-time major semifinalist Tim Henman’s Grand Slam career by beating the Brit in four sets.

French Open runner-up Ivanovic earned another shot at Venus Williams, who beat her in the Wimbledon semifinals. Two-time U.S. Open champion Williams was never really challenged in a 6-1, 6-2 win over No. 21 Alona Bondarenko.

Williams’ younger sister, Serena, reached the fourth round by beating No. 27 Vera Zvonareva 6-4, 7-6 (4). Serena Williams was bothered by the chair umpire’s insistence that she put away a little notebook with handwritten reminders.

“I was like, ‘Well, it’s not like I’m Harry Potter, and my dad can magically give me notes to read,”‘ she said. “It’s something that I write myself. Just little things.”

Her opponent will be Wimbledon runner-up Marion Bartoli, while No. 1 Justine Henin next plays No. 15 Dinara Safina, who ended the run of Ahsha Rolle of the United States, 6-4, 6-3.

Safina’s older brother, 25th-seeded Marat Safin, didn’t put up much of a fight in a 6-3, 6-3, 6-3 loss to Stanislas Wawrinka.

Wawrinka now meets 2005 semifinalist Robby Ginepri of the United States.

Another American, Mardy Fish, led No. 8 Tommy Robredo 4-1 in the fifth set before dropping the last five games and the match, 6-4, 3-6, 6-4, 6-7 (7), 6-4.

That one was played in Arthur Ashe Stadium and lasted 31â2 hours.