Hana Mandlikova, perhaps the most mysterious artiste in tennis, was lucky to advance past the second round Saturday. Today, she was not so fortunate, smacking shots into the net and the fence on her way to a 6-1, 7-6 (7-5) loss to Elizabeth Sayers Smylie.

"I tried hard but I wasn't eager or hungry," Mandlikova said, enigmatic as ever. "It shouldn't have happened, but it happened. I'm disappointed, very disappointed."

Smylie, 22, had watched fellow Australian Dianne Fromholtz Balestrat push Mandlikova to the brink Saturday and believed she could beat Mandlikova, the third seed here and tennis' answer to Dr. Jekyll and Mr. Hyde.

"I really thought Dianne had her on Saturday but she let up just a bit," Smylie said. "I figured if I just made her hit a lot of balls she might do something stupid or make a mistake. I felt going in I had a good chance, and I was right."

Mandlikova's embarrassing loss to the No. 55 player in the world might have been the major upset of this sun-drenched day, but it certainly didn't produce the most exciting tennis. That came on Court No. 1, where Boris Becker and Joakim Nystrom, picking up a match stopped by rain Saturday at one set all, dueled through a fifth set that had more momentum shifts than most football seasons.

In the end, it was Becker, the 17-year-old West German phenom, who had the extra grit needed to survive, 3-6, 7-6 (7-5), 6-1, 4-6, 9-7.

Twice, Nystrom served for the match after breaking Becker. Twice, Becker broke back. Finally, leading by 8-7, already having botched a match point at 7-6, Becker broke for the match, getting to match point with a powerful forehand, then winning the match with a backhand return that Nystrom netted.

Becker's victory over the No. 7 seed is another step in what seems an inevitable rise to the top of the men's rankings. Asked if he was thinking about reaching the top five, Becker shook his head.

"I'm just glad to play well at Wimbledon," said Becker. "To beat the No. 8-ranked player in the world at Wimbledon is exciting. To think past that is a mistake."

Not that John McEnroe and Ivan Lendl are ready to step aside. Both reached the round of 16 today. McEnroe, playing on Court No. 2, stayed calm for most of his match against South African qualifier Christo Steyn and took a 6-3, 7-5, 6-4 victory.

Lendl, who has not looked sharp on the grass, struggled for two sets before taking command against Israel's Shlomo Glickstein, winning 7-6 (7-5), 4-6, 6-4, 6-3. He moves on to what could be a tough fourth-round match against the much-improved Henri Leconte. Today, Leconte finished off a 5-7, 6-3, 6-4, 6-4 victory over John Lloyd, the host nation's last hope in the men's competition.

Yannick Noah, seeded No. 11, was upset by Vijay Amritraj, 4-6, 7-6 (7-5), 6-3, 7-6 (7-3), leaving seven seeded men in the competition.

The other seeded men to play today were No. 5 Anders Jarryd and No. 14 Stefan Edberg. Jarryd routed Vince Van Patten, 6-3, 6-3, 6-1, and Edberg easily beat Chip Hooper, 6-3, 6-4, 6-4, to move on to a round of 16 match against Kevin Curren.

Also reaching the round of 16 were Sammy Giammalva (who will play Jimmy Connors), Danie Visser (who beat Greg Holmes, 10-8, in the fifth set) and qualifiers Ricardo Acuna and Robert Seguso. The latter two will meet each other, guaranteeing a qualifier in the quarters.

And, finally, the odyssey of Vitas Gerulaitis came to an end. Gerulaitis, 31, is as blond and dashing as ever, but hardly the player who made the semifinals here in 1977 and 1978.

Still, he survived two five-set matches to reach the third round. This afternoon, out in the wilderness on Court No. 5, Gerulaitis played yet another five-setter, losing to Heinz Gunthardt, 6-3, 6-7 (8-6), 6-1, 3-6, 7-5. Gunthardt also makes the round of 16.

Lloyd's loss leaves Jo Durie as the only British player still involved in singles play. Durie beat Elise Burgin, 7-5, 7-5, today to reach the round of 16. She joined Chris Evert Lloyd, a 6-2, 6-1 victor over Jenny Byrne; fourth-seeded Manuela Maleeva; fifth-seeded Pam Shriver; 11th-seeded Steffi Graf and 16th-seeded Kathy Rinaldi in the fourth round.

The only seeded woman other than Mandlikova to fall today was No. 14 Wendy Turnbull. Her 2-6, 7-5, 6-1 loss to Pascale Paradis hardly was a shock because Paradis is much improved since she began training with Virginia Wade.

While her charge was winning on an outside court, Wade was making perhaps her final Centre Court appearance, scaring Shriver before losing, 6-2, 5-7, 6-2. Wade even had a break point leading, 2-1, in the third set.

Shriver saved the break point and won the last four games. Wade left with cheers ringing in her ears and many memories to look back on after 24 years and 199 matches at Wimbledon.

McEnroe also departed to loud cheers today. He had been upset Sunday when he learned he had been scheduled for Court No. 2. "I really don't think any defending champion should play outside," he said. "I think you should have to lose on one of the show courts. But with the matches backed up by the rain, maybe the committee had to do it."

Steyn, 20, ranked No. 201 in the world, beat 1983 finalist Chris Lewis to reach the third round. He has a strong grass court first serve. McEnroe did most of his damage off the second serve. After rolling through a first set in which he lost four points on his serve, McEnroe had to struggle in the second set.

After going up a break, he fell back to even, then botched seven break points in two games. Finally, at 5-5 on break point eight, McEnroe charged in on a deep forehand and Steyn, going for a perfect shot, pushed a backhand wide.

McEnroe served out the set, survived four break points in his first service game of the third set and got the break he needed when Steyn netted a forehand volley while serving at 2-all.

Meanwhile, Becker and Nystrom were wowing them on Court No. 1. This was an eye-for-an-eye match, two players unwilling to back down from one another. Becker was going to come to the net and Nystrom was going to pass him.

It looked as if Nystrom's experience would finally win the day when he broke with a gorgeous backhand down the line to lead, 5-4, in the fifth. Serving for the match, he quickly led, 30-0. But Becker didn't flinch.

He smacked a backhand return and got to 30-all when Nystrom missed a volley. Then came the crucial point of the match: Nystrom got in a twisting serve, and Becker, gambling, chipped and came in. Nystrom, following his serve, had the whole court available for a backhand volley. He missed.

"I think that's where the match was decided, when I missed the volley for match point," Nystrom said.

After Becker broke with a ripped backhand, Nystrom broke right back to lead, 6-5. This time Becker broke back at 15, going for corners on every return.

Becker could have won the match at 7-6, but with an easy forehand volley, he got too cute, trying to play a touch, angle volley. Nystrom slammed it cross court to stay alive. But, two games later, after double-faulting to 15-30, Nystrom had no answers for Becker's last two shots.