NEW YORK, AUG. 28 -- There are just some days when Stefan Edberg's deliberate game turns to slow-footedness and his smooth strokes become leaden. This was one of them, the most unfortunate of afternoons for him as it happened because the mercurial, top-ranked Swede was a straight-set loser to Alexander Volkov, a voracious if unseeded talent from the Soviet Union, in the first round of the U.S. Open at the National Tennis Center.

Perhaps it was unwise to make Edberg the top seed in the Open, a tournament that irks him so much he has made just two semifinals in eight years, but he was flush from his Wimbledon triumph and on a 21-match winning streak, and when he is on his form it is the most debonair in the world. Few would have predicted that Edberg's game would turn to such junk in a single afternoon, and that the equally moody Volkov would switch on the lights like this en route to a 6-3, 7-6 (7-3), 6-2 win.

Edberg became the first men's top seed to be upset in the opening round of the tournament since John Newcombe was defeated by Jan Kodes in 1971, and only the sixth ever. But even with the unpredictablility of Volkov, a 23-year-old ranked No. 52, and the vacant, loose play of Edberg, the upset lacked true surprise.

Really, no one is ever earnestly taken aback when the withdrawn, 24-year-old Edberg loses, as his chief weakness has always been a placid susceptibility to upset. He was defeated in the first round of the French Open in May by Sergei Bruguera of Spain. That occasion was the first time a top seed had been eliminated in the opening round in French Open history.

Edberg also lost in the first round here in 1983 to Aaron Krickstein, in five sets. Last year, he was upset by 37-year-old Jimmy Connors in straight sets in the fourth round.

"This is something you need to sit and think about," Edberg said. "At the moment, I can't tell you too many reasons because I don't know myself. You just think it over and try to figure it out so it doesn't happen again."

There was at least one person who was stunned by the turn of events at Louis Armstrong Stadium: Volkov, who raised his game to a startling new level in a single afternoon. The 23-year-old Soviet, who comes from the Baltic seaport of Kaliningrad, did not take the game up until he was 10, a natural left-hander who used to play with two-fisted strokes fron both sides. His reputation is as a player who alternates brilliance with sloppinesss and has a habit of losing leads.

"I don't know when I'm going to play well," he said with a shrug. "I know I have a chance, because it's tennis. But I did not expect a win this easy."

When Volkov learned his first-round opponent would be Edberg, he assumed he would be the loser and committed to play a match Friday in Berlin. Instead he lashed out relentlessly today, making hardly a mistake. He had a total of 30 winners, 11 with a high two-fisted backhand from ear level, and six aces. And just 12 unforced errors.

"Maybe I change my plans now," he said. "I was going to be on Lufthansa tomorrow. I would like to win another match. We will see."

Edberg used up whatever upset dust there was in the air. John McEnroe, the four-time champion who is unseeded for the first time in 12 years, was thought to be a potential victim of Javier Sanchez of Spain. But McEnroe, who was a first-round loser at Wimbledon and has been idle for much of this season, demonstrated that his umpteenth attempt at a comeback may be working with a 7-6 (10-8), 7-6 (7-3), 6-4 win.

McEnroe committed 21 unforced errors in the first set before he began to show some of his old touch, killing a set point with a drop-shot winner in the first tiebreaker. He was as high as No. 4 last year, but has fallen to No. 20 and is still scraping the rust off of his game. Like Volkov, he admitted a single match victory did not necessarily promise another one. He would not even discuss his chances of winning the tournament.

"I think that's sort of ridiculous," he said.

Ivan Lendl also is using this tournament as a comeback of sorts, having dropped to No. 3 in the world after 80 weeks at No. 1, and seeking to make a record-breaking ninth consecutive Open final. Idle following his failed drive to win the Wimbledon title that has eluded him, Lendl lacked his usual relentless consistency today and trailed Martin Laurendeau of Canada by 1-4 in the first set before collecting himself for a 7-5, 6-2, 6-2 victory.

It was not an auspicious beginning against a player who is ranked seventh in Canada. Lendl was good on just 58 percent of his first serves and committed 23 unforced errors to Laurendeau's 30.

"I wasn't particularly worried about it because I could see very clearly how I got there," Lendl said. "I was missing. But I was hitting the ball crazy, so I knew I would eventually get more in and I should be fine."

Otherwise, the seeded players advanced safely. No. 4 Andre Agassi defeated Grant Connell of Canada, ranked No. 90, in three almost uniform sets, 6-4, 6-2, 6-2. No. 11 Michael Chang defeated onetime French Open finalist Mikael Pernfors of Sweden, 6-0, 6-2, 6-3.

There were no upsets or troublesome matches at all among the women. Second-seeded Martina Navratilova knew absolutely nothing about Federica Haumuller of Argentina before their match, and didn't hang around long enough to find out much as she won by 6-4, 6-0. Fourth-seeded Zina Garrison also encountered an obscurity in Beate Reinstadler of Austria and dispatched her, 6-1, 6-3. Jennifer Capriati made her Open debut tonight, defeating Anke Huber of West Germany, 7-5, 7-5, winning a battle of 14-15-year-olds.

Everything seemed routine after Edberg's loss, which came in the first match of the day. When Volkov broke the Swede's serve in the eighth game of the match and held his own serve to take the first set, there was only a small ripple of concern. "He can play great, but he can also play badly," Edberg said. Then Volkov broke Edberg again in the second game of the next set for a 2-0 lead, the Swede contributing a double fault on break point. They swung back and forth into the tiebreaker.

Volkov raced to a 4-0 lead with an ace, a serve winner and a ripped forehand return that ticked the line. He created set point, 6-2, with a similarly huge forehand return. Edberg saved it with a serve winner wide to the backhand, but then it was Volkov's serve, and he spun the ball deep to Edberg's backhand, the Swede driving it into the net.

"I wasn't moving well," Edberg said. "I felt slow out there, and that will make you feel in a rush, like you can't get to the ball in time. So you say, 'What shall I do now? What is wrong?' "

The second set was the decisive one of the match, because Volkov broke Edberg again in the fourth game of the third. He broke him again for the match, with a blasted backhand return down the line for a winner, and then another driving backhand return at the Swede's oncoming feet. Edberg lunged and shoveled it into the net with a forehand volley.

It had seemed with his Wimbledon victory and subsequent streak that Edberg had laid to rest charges that he lacked competitive heart. Now it appears he must face the accusations anew. But Edberg defended his record.

"I don't feel the same way this time because this has been one of my best summers," he said.