For two years, Rafael Nadal has been the most frustrating opponent in tennis. The 20-year-old Spaniard runs, slides, twists, and never, ever stops, no matter the surface, no matter the hour, not matter the score. After playing Nadal, many a man, including one named Roger Federer, has headed to the showers feeling like he has spent three hours banging his head against a wall.

Not Mikhail Youzhny. The 24-year-old Russian was something of a surprise quarterfinalist, having played .500 tennis — 18 wins, 18 losses — prior to the U.S. Open. As a semifinalist with a 6–3, 5–7, 7–6(5), 6–1 victory over Nadal, the no. 2 player in the world, Youzhny is a certified shocker.

Nadal, as one would expect, did not quit. But each time he flung a ball over the net, Youzhny all but begged him for another. He slugged forehands left, center, and, mostly, right — challenging Nadal’s lefty forehand. Each rally, it seemed, Nadal took one step back and then another, until he was 10 feet behind the baseline and Youzhny was six inches inside it, belting forehands and whipping his one-handed backhand cross court for winners.

Youzhny played superb at the most important moments. In the third set, he salvaged his service game at 4–5 after falling behind 0–40. In the third-set tiebreaker, Nadal led 5-4 when he clipped the net with a forehand. It jumped up and sailed long, and Youzhny won the next two points. Thirty-one minutes later, he had finished off the match and offered the crowd his own rendition of Andre Agassi’s trademark kisses: a military salute, with his racket held on his head like a cap.

“I think it’s really Russian, what I am doing,” he said.

Though he had never survived the fourth round of Grand Slam event before this tournament, Youzhny has some experience with tense matches. In 2002, he won the decisive Davis Cup match against France in four hours and 27 minutes, recovering from a two-set deficit to give Russia its first ever title.

As important as that victory was for his country, Youzhny did not enjoy it. Three months before, his father died.

“It was very tough time,” he said.

This victory, Youzhny could enjoy, and Nadal was happy to let him. Having lost on court, the two-time French Open champion and Wimbledon finalist continued to show his winning personality off of it. He would not blame the ankle pain that bothered him during his last match. Yes, he could have been calmer on a few crucial points, and yes, Youzhny was fortunate to escape the third set. Without a doubt, Nadal said, this was the best match of his career at the U.S. Open. Youzhny had simply beaten him.

“No ankle, no pain, nothing,” Nadal said. “I lose. He play better than me.”

While Youzhny will not play again until Saturday afternoon, the other four men who won their rain-delayed matches will return to action today.

Foremost among them are Federer, who defeated an unexpected opponent, Marc Gicquel, 6–3, 7–6(2), 6–3, and James Blake, who played his best tennis of the tournament against Tomas Berdych, winning 6–4, 6–3, 6–1.

Berdych is a behemoth of a man — 6-foot-5, 200 pounds — and no one on the tour strikes the ball as fiercely. His temperament, however, is suspect. Once he fell behind, the 20-year-old from the Czech Republic seemed to lose interest in the match. By the middle of the third set, frustration had settled in. He failed to win a single break point in eight chances in the second set, and missed another seven in the third.

The victory gave Blake a return trip to the quarterfinals, once again under the lights of Arthur Ashe Stadium. Last year, he lost to Agassi in the best match of the tournament, a five-set affair whose final tiebreaker ended with a trademark forehand return winner from Agassi. This year, Blake will have an even more difficult test: Federer.

“If I beat him, it sure as heck doesn’t mean I’m the best player in the world, but maybe for a day, I’ll think that,” Blake said. “If I lose to him, there’s clearly no shame in that.”

So far this tournament, Federer has lived in the shadows. Twice he has played in Louis Armstrong; on Sunday, he did not take the court until after 9:00 p.m. He plays the most exciting tennis in the world, and yet few people have seen his face this year. Tonight, millions will have their first chance.

The winner of Federer and Blake will face another unlikely semifinalist, and possibly another Russian.

Nikolay Davydenko, a man who plays a tournament almost every week, does not have quite the firepower of Youzhny, but he makes up for it with speed and stamina. Yesterday he wrote a quick ending to a continued match with Andy Murray, smothering the young Scot in the final set, 6–1, 5–7, 6–3, 6–0. His next opponent, Tommy Haas, won the match of the afternoon against his hitting partner and friend, Marat Safin, 4–6, 6–3, 2–6, 6–2, 7–6(5).

Haas played flawless in the final tiebreaker. Safin was careless: he missed an easy volley and hit another one too softly, giving Haas a chance to hit a spectacular lob. Unfortunately for Haas, he might need another five sets to defeat Davydenko. Let the running begin.