They pushed their beleaguered bodies this way and that for 4 hours, 44 minutes today, 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 en route to the title. Two-time U.S. Open champion Williams was never really challenged Friday night in a 6-1, 6-2 victory over No. 21 Alona Bondarenko.

Williams' younger sister, Serena, got to 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. Safin then was reminded that Pete Sampras predicted the Russian would spend many years at No. 1 after winning the 2000 U.S. Open.

"Even the geniuses make mistakes," Safin said.

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.

Fish's explanation? "I froze," he said.

That one was played in Arthur Ashe Stadium and lasted 3› hours, which seemed like nothing in comparison to what went on over at Louis Armstrong Stadium.

"I am totally exhausted. No energy. I smell my shoes — they are so stinky," Djokovic said, then noted that he was fighting cramps "in both of the legs and an arm and back and head."

He got his upper legs massaged a few times. During one break, he plopped down on his stomach so a trainer could knead Djokovic's lower back. Stepanek, too, needed help at changeovers.

Yet both just kept going, remarkably combining for only 88 unforced errors despite the number of shots they hit.

Somehow, both found the strength to play to the crowd, waving their palms or cupping a hand to an ear to ask for louder cheering. Djokovic celebrated a couple of big points by leaping high with a scissor-kick and an uppercut.

On one marvelous exchange, Djokovic's shot clipped the net and barely went over, but Stepanek raced to get the ball and slap it across his body. Djokovic got to that, forcing Stepanek to race back to the baseline for a defensive lob that Djokovic simply tapped in for a winner. Djokovic then let his racket fall so he could do a quick jig.

At 4-4 in the fifth set, Stepanek flubbed a shot and mocked himself — and, perhaps, Djokovic — with his own two-step.

Spectators regaled Djokovic and Stepanek with standing ovations during changeovers, before the fifth-set tiebreaker and, of course, at the finish.

Stepanek might be best known for having recently been engaged to five-time major champion Martina Hingis — and for having a tour spokesman announce the wedding was off.

The 20-year-old Djokovic, on the other hand, is quickly gaining popularity, thanks to his engaging personality and his YouTube-posted impersonations of other players.

Ah, yes, and his results. He reached the semifinals at the French Open and Wimbledon, and beat then-No. 3 Andy Roddick, Nadal and Federer at Montreal, the first player in 13 years to defeat the top three men at a single tournament.

"I had some impressive results this year," Djokovic said. "Of course, the people expect me to do well."

He didn't disappoint Friday.

The U.S. Open is the only Grand Slam tournament that uses a tiebreaker to end fifth sets, and Stepanek compared it to playing the lottery.