Vitas Gerulaitis already had lost a set and was down, 0-3, in the second-set tie breaker when he walked to the wrong court to serve. "Mr. Gerulaitis," the umpire murmured gently, nodding in the right direction.

Gerulaitis, the fifth-ranked player in the world, the fifth-seeded player in the U.S. Open, just didn't seem to be all there. "Oh, I was there," said Gerulaitis, who had not lost in the Open's first round since 1973. "I was just thinking about the next point. I thought maybe they would give me an extra point and it would be 3-1."

The next three points went to Gerulaitis. But the tie breaker and the match went to Fritz Buehning, the 56th-ranked player, who sometimes plays so much better than his ranking, 6-4, 7-6 (7-4), 6-3.

The day was equally unkind to Jose-Luis Clerc, the seventh seed, who lost to Kim Warwick, the 55th-ranked player, 3-6, 6-4, 1-6, 6-1, 7-6 (7-3). Warwick tore a tendon in his right shoulder playing John McEnroe in June 1981 and retore it in February. This was only his second victory in seven matches since returning to play. "The other guy I beat was Mike Myberg, household name, huh?" he said.

The second day of the open featured two upsets, four rain delays, and one power outage that caused the postponement of the John McEnroe-Tim Gullikson match at 3-all in the first set. Just as the power was restored, the rains came, and the tournament called it a night.

The walking wounded in the women's draw fared well. Tracy Austin, the No. 2 seed and defending champion, who developed tendinitis in her right shoulder Thursday, was leading Catherine Tanvier, 6-2, 4-1, when Tanvier, ironically, had to retire because of a turned right ankle. Austin said both her shoulder and her play were "okay." Nothing better, nothing worse.

Andrea Jaeger, the No. 4 seed, who has a groin pull, appeared to be moving well as she beat Lena Sandin, 6-1, 6-1. Then, again, she didn't have to move too much at all.

The two Wimbledon winners, Jimmy Connors and Martina Navratilova, won their first-round matches with ease and dispatch. Connors, No. 2 seed, started slowly but beat Jeff Borowiak, 7-6 (7-5), 6-2, 6-3. Navratilova, seeded No. 1, beat Laura DuPont, 6-1, 6-1, in 42 minutes. By her own account, Navratilova didn't miss a volley. She looked very much like someone who is 65-1 this year.

If she wins the Open, which she has never done, she will have won all four Grand Slam events in the space of 12 months. Asked if she would consider this winning the Grand Slam (though there is no rule, most officials say you have to win all four in one calender year), she said, "I'll leave it up to you guys. If I have to go to Australia, I will."

Clerc's and Gerulaitis' power shortages were more critical than those affecting the facilities.

Clerc, who had such a spectacular summer of 1981, winning four tournaments in a row before losing in the fourth round of the Open, will not look back fondly on the summer of '82. He lost in the semis of three of the four tournaments he won a year ago, and defaulted to Warwick in the first round at La Costa. It never would have happened if Warwick's doctor had had his way. After Warwick reinjured his shoulder, the doctor told him not to play again. What did you do then? he was asked. "I got another doctor," he said.

The first point of the fifth-set tie breaker may have proved the difference between them. Clerc missed his first serve. On his second, Warwick chose to go for it, hitting an outright winner on a backhand cross court, rather than opting for just keeping the ball in play.

He won the next three points before Clerc got a service winner to make it 4-1, Warwick. Warwick hit a forehand cross court volley to go up, 5-1, and a lovely serve wide to Clerc's forehand, which Clerc could not return. It was match point.

Clerc did not readily give in to the inevitable. He hit a service winner to make it 2-6, and an ace to make it 3-6. But then with Warwick serving once again for the match, Clerc mis-hit a backhand, which dribbled toward the net.

Against Gerulaitis, Buehning went for everything, hitting out, hitting unreturnable serves (he got in 57 percent of his first serves). Everything he did seemed under control, including his temper, which is legendary. Buehning did not want to let Gerulaitis get his rhythm. He never did. Gerulaitis never got his first serve under control either (he got in only 41 percent of them). "Nothing clicked," Gerulaitis said.

Even after Gerulaitis managed to knot the tie breaker at 3, he could do nothing. When Buehning hit an overhead that Gerulaitis managed to run down behind the base line, his return went just wide. He looked up, as if to say, "What can I do?"

"He lost heart after that," Buehning said. "That broke his back."

Buehning, who had beaten Gerulaitis only once before, quickly took a 3-0 lead in the third set, breaking in the second game and holding in the third. Gerulaitis broke in the fifth game to make it 3-2. "I guess I thought, 'I've got him now' and let up a little," Buehning said.

But he broke in the sixth and held serve in the seventh to go up, 5-2. With Buehning serving for the match at 5-3, 30-30, Gerulaitis stretched for a forehand volley. It hit the cord and took its sweet, agonizing time, bouncing back towards Gerulaitis. It was match point. "It was one of those days," Gerulaitis said.

Gerulaitis's name has been mentioned in testimony in federal court in connection with a cocaine investigation. But there are no charges against him. On Tuesday, he said those reports would not affect his concentration. But Buehning wasn't sure. "Mentally, it may have," Buehning said. "When you walk on the court you forget. But maybe a problem like that or a family problem sticks in the back of your head. A few guys in the stands said a few things and maybe he got upset. I don't know."