It was a typical first day at the U.S. Open: upset and upsets. John McEnroe, the No. 1 seed, unnerved and extended by Trey Waltke, won his match but lost his cool, throwing a handful of sawdust and many epithets at a fan he thought had come to abuse him.

McEnroe finally prevailed, 6-3, 5-7, 4-6, 6-0, 6-1, and said he was sorry. "The guy was egging me on," he said, "clapping when I double-faulted. I still think I was wrong to say bad things to them. But I think people like that shouldn't come to tennis matches."

Chris Schneider, a high school basketball coach from Long Island, at whom the sawdust was thrown, said, "I was clapping and rooting and cheering for the underdog," but only at appropriate times. At one point McEnroe turned and asked him, "Haven't you got anything better to do than hope I miss the ball?"

"I said, 'No,' " Schneider said. "He referred to me as being sick and ill." Another fan, sitting close by, urged McEnroe to concentrate, but when the player told him succinctly to mind his own business he, too, began to cheer Waltke. McEnroe said "Obviously, I snapped a little bit."

McEnroe was fined $1,850--$1,000 for abusing the spectators, $500 for verbally abusing umpire Stu Saphire of Washington, D.C., and $350 for abusing the ball. His fines for the year now total $7,300, $200 short of the limit that would give him a mandatory 21-day suspension.

There was more. Tracy Austin, the fourth women's seed, who has been plagued by injuries for the last two years, withdrew from this tournament and the next three she was scheduled to play in because of a rib injury. Austin, who also withdrew from Wimbledon this year, has not played in a tournament since losing in the quarterfinals of the French Open in the spring.

It was too much emotion for the first round. Tim Wilkison, who is ranked 73rd, upset eighth-seeded Jose-Luis Clerc, 6-2, 6-3, 7-6 (7-4). After it ended on a controversial call, Wilkison heaved the ball skyward, thrust his fist in the air, pounded the net with his racket and screamed, "Yesssss!!!!" He could almost be heard over the jets flying above the stadium.

Clerc stood at the base line, his racket at his feet, staring at the spot where he was sure Wilkison's volley had gone wide. It was the second match point of the tie breaker. Wilkison hit a backhand volley, Clerc was certain it was wide, lobbed it lamely and stood still as Wilkison put away the overhead.

Clerc said the shot was as wide "as my guts." He fares well everywhere but in the biggest events. He now has the dubious distinction of having lost in the first round of Wimbledon and the U.S. Open and the second round of the French Open, all in one year. But he seemed as stoic as Wilkison was exuberant. "He is so crazy, this guy," Clerc said with obvious exaggeration. "He has won one match in three years, so he got so excited today that he won a match."

Wilkison, who lost to Clerc, 7-6, in the fifth set here two years ago, agreed the ball was probably wide, but he wasn't giving an inch, much less a foot. Clerc, who is not at ease or at home on the hard court Deco Turf surface, simply made too many unforced errors.

Jimmy Connors, the defending champion, was extended to four sets in a night match before defeating Ramesh Krishnan, 6-2, 6-4, 3-6, 6-2.

Vitas Gerulaitis, who lost in the first round last year, as did Clerc, survived a very close call. He saved three match points to beat Marcos Hocevar, 3-6, 3-6, 6-3, 7-5, 6-4.

At least the day was routine for someone: Jimmy Arias, the ninth seed who beat Jonathan Canter, 6-2, 6-3, 0-6, 6-2; for Andrea Jeager, the third seed who needed only 47 minutes to dismiss Betsy Nagelsen, 6-0, 6-2.

It was not a routine day, however for Eric Korita, who won his first match as a professional, beating Brian Teacher, 6-3, 4-6, 6-0, 6-4. Korita decided not to return to college before he left for Venezuela to play in the Pan American Games. He was winning too many matches and losing too much money to stay an amateur.

McEnroe's first round cost him $250 more then he earned for the victory. No doubt, Waltke earned his respect. Waltke is a rarity: he is the only man to wear long flannel pants at Wimbledon, and the only man with two first-round Grand Prix victories over McEnroe.

He left the long pants home today, but brought the same uncanny skill that defeated McEnroe two years ago in Memphis and this year in Las Vegas. "He picks up my serve well," McEnroe said. "He's a smooth-type player."

McEnroe was anything but smooth today. He was sluggish and distracted.

With Waltke serving at 2-all in the third set, McEnroe made an error and heard about it from the fans. He had offered them a truce. Now he offered to fight it out. "He said, 'I'll meet you afterwards and fight you,' " Schneider said. "Then he took the sawdust out of his pockets and threw it."

Sometimes, McEnroe plays better when he is upset. Not today. Waltke, sensing his opportunity, bedeviled McEnroe, hitting shots that seemed to catch every line. Waltke broke at love in the ninth game of the set when McEnroe let a return of a second serve go for love-40. A forehand pass down the line gave Waltke the break.

It was his last. McEnroe sensed Waltke had spent himself, broke in the first game of the fourth set and won eight straight games.

Trey means three. Waltke 's real name is Richard Henry Waltke III. They call him Trey "instead of Richard the III," he said.

Though he played royally for three sets, his third defeat of McEnroe was not to be.