NEW YORK, SEPT. 2 -- John McEnroe's victory became Martina Navratilova's loss at the U.S. Open tonight. The 31-year-old McEnroe reached the quarterfinals by upsetting Emilio Sanchez over five sets through 4 hours 20 minutes. Second-seeded, 33-year-old Navratilova was upset by the long wait to take the stadium court, her own lack of ambition and Manuela Maleeva-Fragniere in the fourth round at the National Tennis Center.

Navratilova and McEnroe are aging champions who may not make many more appearances at the Open. Navratilova, contented and drained by her record ninth Wimbledon victory, had little more to play for and could not summon any conviction against Maleeva-Fragniere. The ninth seed who had never beaten her in 13 previous meetings finally did, 7-5, 3-6, 6-3.

Navratilova lost a 4-1 lead in the first set and dropped three straight games despite holding game points in the third set. It was an appalling loss that bespoke how little of her heart was in the tournament after her determined year-long effort to claim a record ninth Wimbledon title. Exactly a year ago Navratilova dismissed Maleeva-Fragniere in the quarterfinals here, 6-0, 6-0.

"I don't want to get too philosophical after a loss like this, but I don't know if the desire will ever be there 100 percent again," Navratilova said.

It has been strangely revived in McEnroe, who has not won a Grand Slam event since 1984. Unseeded for the first time in 12 years and promising to play just one more season, he was urged on by the thought of one last victory and the swelling pandemonium of the stadium as he survived seventh-seeded Sanchez, 7-6 (8-6), 3-6, 4-6, 6-4, 6-3.

McEnroe is thus a surprise quarterfinalist for the first time since 1987, and this is getting serious. He stalked, he circled, he fluttered and he shook his fist for 63 clean winners, and here is the amazing thing: He can win this tournament.

"It put me in another gear," he said. Or was that "year"?

McEnroe's victory and Navratilova's loss combined to make this a certifiably crazy Open. The first week of play was upset-ridden and constantly surprising, beginning with the first-round losses of top-ranked Wimbledon champion Stefan Edberg and French Open titlist Andres Gomez, and the third-round upset of women's French champion Monica Seles.

It was thought that the Open would determine who is No. 1 from among top-ranked Steffi Graf of West Germany, No. 2 Navratilova and No. 3 Seles. Instead it has become anybody's tournament, played out in an unsettled atmosphere and peopled with strange upstart characters like Maleeva-Fragniere, a native Bulgarian ranked No. 9 who suddenly erupted for 39 winners and the most significant victory of her career.

"It means everything I've played for all these years," she said. "It's probably what I've lived for in my tennis career."

The atmosphere was part of Navratilova's problem. She and Maleeva-Fragniere lounged in the locker room during McEnroe's interminable match. Navratilova practiced and ate a bagel. And another. Maleeva went out three times to warm up, and returned. When they finally arrived, the crowd was flat and emotionless after the drama of McEnroe's comeback, and so was Navratilova.

She was bothered by the oppressive humidity that fogged her glasses, stared at the bustling crowds that surrounded actor Tom Cruise, blew overheads, floated paceless volleys deep and double-faulted for 37 unforced errors. She had her serve broken eight times by a normally unmenacing baseliner in Maleeva-Fragniere.

"I think Wimbledon took so much out of me that I really had a hard time," she said. "I wanted to be up but I just couldn't kick it in gear."

Serving at 5-6 in the first set, Navratilova fell behind, 0-40, on an array of mistakes, then Maleeva-Fragniere made a running forehand pass of a listless volley to grab it away from her. Navratilova took the second set largely because Maleeva-Fragniere's nerve failed her, with double faults twice on the last two points.

Navratilova could hardly take confidence from that, and Maleeva-Fragniere struck real fear in her when she broke in just the third game of the final set for a 2-1 lead. It got worse. Navratilova gave up her serve again with an unpardonable performance in the seventh game, unable to hold despite a 40-0 lead. At 40-30, she had the game on her racket with an easy forehand kill to open court, and jerked it wide. "I took it lightly," she said. A mishit overhead and a backhand volley deep gave Maleeva-Fragniere a 5-2 lead.

Navratilova struggled briefly, breaking back, but only to give up her serve the eighth and fatal time. Maleeva-Fragniere created match point with a low, running forehand pass, and Navratilova gave in immediately for the match, with a topped forehand that hit the net cord, bounced lazily in the air and fell back.

This was only the fourth time in 18 years that Navratilova left the tournament prior to the quarterfinals. The last time was in 1980.

Seles' loss to unseeded Linda Ferrando earlier on had seemed to give Navratilova a clear path to the semifinals and a realistic chance at her fifth Open title. Instead, the title is now open to anybody who can challenge Graf, most obviously fifth-seeded Gabriela Sabatini of Argentina, who reached the quarters with a convincing defeat of No. 11 Helena Sukova of Czechoslovakia, 6-2, 6-1.

McEnroe is playing well above his No. 20 ranking. Beating Sanchez, 25, made it two seeded victims in as many rounds, with No. 10 Andrei Chesnokov. He is now on course for a semifinal meeting with Ivan Lendl, the eight-time finalist and third seed who reached the round of eight by defeating Gilad Bloom of Israel, 6-0, 6-3, 6-4. Next, Lendl faces No. 12 Pete Sampras, who stopped sixth-seeded Thomas Muster tonight, 6-7 (6-8), 7-6 (7-5), 6-4, 6-3.

Clearly, McEnroe wants more, and he has every chance of getting it. His next opponent is unseeded David Wheaton, age 21 and No. 44, who beat Kevin Curren, 7-5, 7-6 (7-1), 4-6, 6-4.

"Certainly its nice to win a match like this," McEnroe said. "But it would be even better to take it farther and win a bigger one."

The match turned on the first and fourth sets as McEnroe took leads, lost them and got them back again, struggling in the face of Sanchez's unrelenting consistency, with just 14 unforced errors. McEnroe had a 5-2 margin in the first but needed four set points to close it.

In the tiebreaker, McEnroe went up 2-0, but Sanchez took the next four points, the last an ace. But McEnroe then hit his shot of the match. As Sanchez slammed an overhead at his feet, McEnroe nimbly sidestepped it at the baseline, hopped on one foot and drove a reflex forehand half volley passing shot down the line. That turned the momentum in his favor briefly, but Sanchez took over in the next two sets.

The fourth set was decided in the riotous, chilling 10th game. Sanchez won a cheap point in a toe-to-toe net exchange by pushing a forehand mis-hit volley to open court, and appeared to touch the net. McEnroe argued, Sanchez argued back, and kept the point, 30-30. But Sanchez next pushed a forehand deep on a baseline rally to give McEnroe, still furious, a break and set point as roars erupted. "They were giving me a goodbye hand," McEnroe said. "At that point anything could have happened."

McEnroe strode to the net and shook his fist at Sanchez. He then returned Sanchez's second serve and charged, stabbing three volleys, the last a backhand into open court. As it twisted off the line, McEnroe raised his arms.

"I think he was eager and mentally a little bit better than me," Sanchez said.

The fifth was all McEnroe.