Saturday night, in the privacy of his dreams, Aaron Krickstein thought he had lost to Vitas Gerulaitis. "I think I lost in straight sets," he said. "Right when something happened, I woke up."

Krickstein's dream did not come true. He beat Vitas Gerulaitis, 3-6, 3-6, 6-4, 6-3, 6-4, becoming, at 16, the youngest man ever to get to the round of 16 at the U.S. Open and forcing his parents to change their hotel reservations for the fourth time in a week.

Up a break and serving at 4-2 in the fifth set, Gerulaitis made a miraculous scrambling get of a forehand top spin lob and lobbed back just over Krickstein's head for 40-30. Then Gerulaitis came undone, winning only four of the last 20 points of the match. He double faulted on the next point, lost a game point with another and, on the next point, gave Kriekstein a break point with a third. The kid from Grosse Point, Mich., broke his serve and his will with a backhand cross court pass that nicked the line.

Staring at Gerulaitis, the No. 15 seed who was a finalist here in 1979, Krickstein held at love to even the set at 4-4. Gerulaitis served again and badly. He double faulted to give Krickstein break point, saved it and double faulted again, his 15th of the match. Krickstein led, 5-4. On the change, Gerulaitis unraveled the tape on his racket handle, a telling reminder of what was happening to him.

Krickstein served for the match and won it amid a roar with a two-handed backhand down the line, the backhand Gerulaitis had been working over all day. Krickstein's braces glinted in the light as the two players shook hands at the net. "I think he said, 'good playing,' " Krickstein said.

Gerulaitis said nothing to the press and was fined $1,000. "If I talk to you two, I'll get fined $1,000 anyway," he told two reporters who trailed him. He tossed a Coke can onto the railroad tracks outside the National Tennis Center, made tracks for his Mercedes, and sped away.

It was a day of confrontations between old and young, young and younger. Youth was not always served so well. Andrea Leand of Baltimore County, who is 19, did her part, defeating Wendy Turnbull, the sixth seed, 7-5, 4-6, 6-2. Jimmy Arias, the ninth seed, who is 19, defeated Gianni Ocleppo, 7-6 (8-6), 6-1, 6-2. Later, he said he was playing so badly he couldn't take a game off Carling Bassett.

Bassett, who is 15, couldn't take a set off Zina Garrison, the 10th seed, and lost, 6-4, 6-3. Garrison's mother, Mary, underwent triple bypass surgery two weeks ago. "She is on a kidney machine and she is a diabetic," Garrison said. "The doctors said the bypass went better than they expected."

Garrison withdrew from two tournaments in August. "My mom was pretty close to dying and I didn't want to play tennis," she said. "She said she wanted me to come here and play the best I could."

John McEnroe, the No. 1 seed, tarnished Vince Van Patten's glamor, with a 6-1, 6-2, 6-1 defeat. Ivan Lendl, the second seed, trifled with 20-year-old Jonathan Levine, 6-2, 6-2, 6-2. Chris Evert Lloyd, also seeded second, beat 16-year-old Manuela Maleeva, the French junior champion, 6-4, 6-0. She insists her next round match with Kathy Jordan, who beat her at Wimbledon, "will not be a grudge match."

Eric Korita, who turned pro two days before the Open, lost to Yannick Noah, just as he did last year in the third round, 5-7, 6-3, 6-3, 6-4.

Korita has the blistering serve, but today Noah had more aces (14 to six). "I returned better than last year," Noah said. "Sometimes when I returned, I surprised him but I surprised myself, too."

Noah was at his most acrobatic, though he said the diving gets he made were the result of being late for the ball.

In the fifth game of the last set, Korita fell behind, 15-30, on a double fault, one of eight for the day. He protested the call mildly. Distracted, he fell behind, 30-40, and hit a forehand volley that was called long. His protest was more vigorous but equally useless.

"I think it was good," Noah said. "Usually, I give it back, but it was an important point.

"When you give this kind of point back, you think about it the whole match."

Choices. Krickstein sprained his right patella while winning the national 18s championship in August. He almost decided not to use his wild-card entry into the Open and didn't practice for nine days. With a doctor's permission and his coach Nick Bollettieri's encouragement, he decided to play.

Bollettieri said Krickstein's father, Herb, a pathologist, was reluctant to let his son play. He relented after Bollettieri told him, "There's nothing wrong with the knee."

Krickstein, who beat Stefan Edberg, the top-ranked junior player, in the first round, withdrew from the junior competition here, but his knee didn't seem to bother him today.

Because Krickstein has a remarkably strong forehand, Gerulaitis did the only sensible thing. He served to Krickstein's two-handed backhand, chipped returns to his backhand, attacked the net and waited for the errors (Krickstein had 10 on his backhand in the match). For two sets, it worked.

But Krickstein, who has learned to hold the ball on his racket longer, began to exercise patience. A backhand cross court pass gave him a break point in the eighth game of the fourth set. A sizzling forehand return gave Krickstein the only break of the set.

The fifth set was played amid an uproar in the grandstand. "C'mon Aaron," they yelled. Krickstein, who had never gotten beyond the second round in a professional tournament, began to believe that his time had come. You could see it in his glare. He hit out and hit winners (40 of them). A net game? "Next year," he said.

This year, he moves to Bollettieri's Academy in Bradenton, Fla., where his oldest sister teaches, to train fulltime. And this year, perhaps, he will turn pro. "I'm only sorry he didn't check that box, 'pro,' before the tournament," his father said, laughing. "I didn't have any idea he'd get this far."

If dreams are any indication, neither did his son. "It was sort of weird to wake up," he said.

The world woke up to him today.