PARIS - Hopping in place in a hallway leading to the court, Rafael Nadal was drenched with sweat before he smacked a ball in his French Open quarterfinal.

A study in perpetual motion, Nadal actually got a bit of a breather Wednesday, when Novak Djokovic of Serbia-Montenegro quit with a back injury after losing the first two sets. That put defending champion Nadal into the semifinals at Roland Garros with what goes into the books as his 58th consecutive victory on clay, extending his record.

“The fact that today’s match was, I wouldn’t say ’comfortable,’ but low-intensity, is going to help Rafael,” said Nadal’s coach and uncle, Toni. “It’s great to compensate for the long matches he’s had.”

That’s hardly good news for Nadal’s next opponent, Ivan Ljubicic, who beat Julien Benneteau of France 6-2, 6-2, 6-3 to reach his first semifinal in 27 trips to Grand Slam tournaments.

With No. 2 Nadal facing No. 4 Ljubicic, and No. 1 Roger Federer playing No. 3 Diego Nalbandian on Friday, it’s first time since 1985 that the men seeded 1-4 at the French Open all made the semifinals.

“I don’t think there’s any doubt that (Nadal) is a big favorite. Of the four of us left, he is definitely the favored one,” said Ljubicic, who hasn’t faced a seeded player in the tournament. “Just by reaching the semifinals, I did something incredible. There’s absolutely going to be zero pressure for me.”

The French Open is generally regarded as the most grueling tournament on tour, and this year’s edition apparently was as tough as any: Djokovic’s retirement was the eighth of 2006, the most among men at Roland Garros in the modern era. Like the other majors, it requires players to string together seven victories over two weeks to earn the title. Unlike the others, it’s played on clay, which tends to extend points and matches, making stamina and will as important as superb strokes.

As well-stocked as the 20-year-old Nadal is with all three of those components, even he was grateful to get off the court after fewer than 2 hours Wednesday: He logged more than eight hours over his previous two matches.

“For those of us more used to playing on clay, maybe we resist a little more, but sometimes we have a tough time, too. We feel the pain, too,” he said. “It’s not always easy to play four, five sets with such high intensity.”

What’s that? Nadal feels pain?

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He sure doesn’t show it on court, where he bounces on his toes during the coin toss, sprints to the baseline for pre-match warmups — and then really gets going once play begins, churning up clouds of dirt as he scrambles and slides.

And yet, for a while, the 63rd-ranked Djokovic hung in there on long rallies, winning seven of the first 10 points that lasted at least 10 strokes. And Djokovic actually finished with more winners, 27-20.

Perhaps with that in mind, the 19-year-old Djokovic gave this assessment of Nadal: “He’s the best on this surface, but he’s not unbeatable. That’s for sure.”

Still, Nadal does things few others can. In the ninth game of the match, a seemingly out-of-position Nadal skidded into place for a forehand passing winner down the line. Djokovic, a bit incredulous, watched the ball sail by, then applauded his opponent’s brilliance.

Nadal broke the unseeded Djokovic’s serve to start the second set on the match’s longest point, a 27-point exchange. Nadal conjured up a drop shot that Djokovic couldn’t handle, and the underdog pounded the ball off the court and into the stands. That was part of a run in which Nadal claimed 11 of 12 points to open a 3-0 lead in the set.

Djokovic received medical treatment at the ensuing changeover, lying on a towel for a massage. From then on, he rarely would go more than a point or two without clutching at his back.

Trailing 6-4, 6-4, Djokovic served to begin the third set. After missing a backhand to fall behind 15-30, he shook his head and walked to the net to concede the first major quarterfinal of his career. Djokovic also retired at last year’s French Open, in the second round; this was the first time in the Open era a man had retired at Roland Garros in the quarterfinals or later.

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“It’s not nice to win like that,” Nadal said.

He’ll take it, of course, and plans to work on serving on his day off.

Ljubicic’s serve is his strong suit, and he swatted 13 aces against the 95th-ranked Benneteau. More impressively, Ljubicic broke Benneteau five times in a row to start the match.

A late bloomer, the 27-year-old Croat never was beyond a major’s third round before this season. He reached the quarterfinals at the Australian Open, and now is one step further in Paris.

To make a Grand Slam final for the first time, though, Ljubicic will have to do something no one has done since April 2005: wear down Nadal and beat him on clay.

“That streak has to finish one day, and I hope that’s going to be Friday,” Ljubicic said. “He cannot win forever — everybody knows that.”