Andre Agassi blew a two set lead and seemed to lose a step. James Blake trailed by a set and 5-2. Guillermo Coria fell behind two sets to one and found himself in a shouting match with his opponent, Nicolas Massu. In the end, all three men prevailed on a volatile day at the U.S. Open, an afternoon marked by mood swings, letdowns, and lots of labored tennis.

For Agassi, experience and persistence won out over the smooth strokes of Xavier Malisse, a powerful hitter from Belgium who seemed on the verge of sinking the 35-year-old American when he found his serve in the third set before losing 6-3, 6-4, 6-7 (5), 4-6, 6-2.

For Blake, calmness prevailed over the nerves of Tommy Robredo, who imploded during a 4-6, 7-5, 6-2, 6-3 loss when he had the chance to write an early and unsatisfying finish to the Cinderella story of the Open. For the fans, excitement won out over disappointment and disbelief, as the tournament, buoyed by the success of American players – sans Andy Roddick – will host the all-American quarterfinal contest that had everyone in Flushing abuzz this weekend: Agassi versus Blake, legend versus admirer, tomorrow night under the lights.

“James is an easy guy to like and he’s an easy guy to root for,” Agassi said. “If he’s getting the better of me, I couldn’t wish it for a better person.”

“I think I saw [Agassi] here back when he had those lime green shorts hanging out of the denim shorts,” Blake said, recalling his days as 10-year-old fan. “People didn’t know if his name was Agassi or A-gossi.”

Nineteen years removed from being a teenage sensation, Agassi now wears the shortest shorts on tour, the whitest whites, and the most practical of caps – and only when it’s sunny. When Agassi takes the court, Arthur Ashe Stadium bubbles over with “Johnny B. Goode,” Summertime Blues,” or “Rock Around the Clock,” golden oldies befitting this aging star, or at least his fans. Blake, the young buck, calls his one victory over Agassi, in 2002, the greatest win of his life, and he hopes to get another dose tomorrow night.

“He’s going to go out there and just let it rip,” Blake said. “I’m going to try to do the same.”

Agassi has about the best draw he could hope for as he tries to become the oldest man to win this tournament. Blake, 10 years his junior, has about the best form he could hope for. He is playing the tennis of his life, seemingly surprising even himself with an upset victory over no. 2 seed Rafael Nadal this weekend and a come-from-behind victory yesterday over Robredo.

By the way their matches unfolded yesterday, it would not have been a shock if both of them ended up on the sidelines. Agassi took advantage of an erratic Malisse early, breaking serve twice in the first set and playing clean tennis in the second, in which he needed just one break. As the third set got under way, a fan at Arthur Ashe Stadium picked a quiet moment to inject some humor into the match, telling Agassi, “He’s a punk, you’re a legend.” It was the equivalent of yelling, “Free Bird!” at an Elton John concert: Unlike Jimmy Connors, receiver of the original wisecrack at the U.S. Open against a long-haired Agassi, this legend did not need any help against the longhaired Malisse.

It wasn’t long before the tenor of the match changed, however. Malisse began holding his service games with ease, at one stretch winning 16 of 17 points on serve. He also began returning more aggressively, pouncing on Agassi’s second serve.

Still, Agassi nearly broke serve at 5-5 – clipping the tape – and took a 5-3 lead in the third-set tiebreak. Malisse struck back with a volley winner and two backhand winners down the line. From there on, it was Malisse dictating play, seemingly moving toward his second straight comeback from a two-set deficit. Agassi did what he could to stay in the match.

“I just kept my head down and kept wanting to make him earn it,” Agassi said.

In the end, Agassi calmly ended Malisse’s day, breaking for a 3-1 fifth set lead with a backhand winner down the line. At that key moment, he offered not even a fist pump, not even a smile as the crowd roared in approval. He closed out the match with a slice backhand that Malisse, lunging to his right, volleyed long.

Blake was in deeper trouble against Robredo, a talented clay-courter who defeated Marat Safin at this year’s French Open. The Spaniard kept Blake on the defensive for two sets with a sharp one-handed backhand and impressive footwork and touch around the net. He found himself a point from the second set before Blake had even settled into the match, but his collapse was just as quick.

Serving at 5-3 in the second set, Robredo double faulted twice, giving Blake new life. Soon, the forehand that muscled the hulking Nadal out of the tournament had reappeared, and Blake began to roll.

“I think it was a really easy match for me, and then I had the chance and I didn’t get it,” Robredo said.

Coria, one of two Argentine’s remaining in the draw, overcame 20 double faults and insinuations from Massu that he was faking a toe injury. During one changeover, the two jawed at each other, with Massu standing in front of the seated Coria and shouting. The dispute continued as a tournament official stood between them. Massu, who held a two-sets-to-one lead, lost control in the end, falling 6-4, 2-6, 6-7 (5), 6-2, 6-2.