WIMBLEDON,ENGLAND, JULY 3 -- The last thing a favorite wants to see across the net is Zina Garrison's restless rocking and hatchet-like slices. Garrison can ruin all assumptions and overturn any sure thing; the problem is whether she can become surer of herself.

The fifth-seeded Garrison's defeat of third-seeded Monica Seles today to reach the Wimbledon semifinals may have been more than just another flashy upset for the 26-year-old veteran from Houston. Garrison overcame a one-set deficit, a painful fall to the grass and a match point against her to win after 2 hours 22 minutes, 3-6, 6-3, 9-7.

The No. 5 player in the world has long struggled to acquire composure, perhaps the missing element that has prevented her from making the final of a Grand Slam event. Against Seles she found a measure of it, pressed by the thought of four disturbing losses this season in which she let leads get away. She reeled off three forehand winners that turned the momentum in the 14th game of the final set.

"I've been in situations to win and I didn't win it," Garrison said. "I just kept saying to myself that I was overdue and I was going to hang tough, and the shots started to fall my way."

Garrison was rarely considered in all the speculation over who might prevent Steffi Graf from repeating as Wimbledon champion. If there were going to be an upset, it was considered more likely to come in a semifinal meeting between Graf and 16-year-old Seles, the French Open champion who was on a 36-match, six-tournament winning streak before today's loss.

But Garrison, who plays Graf in the semifinals Friday, should not have been ignored, given her history. She was a semifinalist here in 1985, and her awkward flat strokes and quick-handed volleying make her a menacing grass court player. The problem was living up to her potential, with two second-round defeats and a quarterfinal appearance since then. In this tournament she has drawn all the elements together. She had lost just 15 games without dropping a set prior to this afternoon.

"I always felt I'm a really good grass court player," she said. "I just never really did as well. I think I have a better chance this year because I'm playing within my older self. I'm 26. I'm an old person on the tour now."

Garrison has a long list of unwitting victims, dating from 1982 when she defeated Evonne Goolagong here in the second round. In 1988, she sent Gabriela Sabatini reeling from Wimbledon in the fourth round, then upset Martina Navratilova in the quarterfinals of the U.S. Open.

Garrison will endure in the record books as the likable villain who ended Chris Evert's career. She defeated Evert in the quarterfinals of last year's U.S. Open, sending the former champion into retirement. It was typical of Garrison that she did so in tears, more emotional perhaps than Evert.

Another crying jag constituted one of Garrison's least pleasant on-court experiences, because it summed up her rather vulnerable nature and susceptibility to pressure. In 1984 she lost in the second round of Wimbledon to home favorite Virginia Wade in a tense, rain-interrupted three-setter. She cried through virtually the entire match.

"It was a very emotional match, and it was a match a lot of people will never forget because I was used, psychologists used me, as an example of getting emotionally upset under pressure," she said. "I just couldn't handle it. I think since then I've grown a lot. I've learned discipline on the court and I've been able to compose myself a lot more."

When Seles held a match point against her in the 14th game, Garrison reacted with a lethal calm. She forced a forehand down the line past Seles, then went on to hold serve while the teenager who is noted for her comebacks was the one who collapsed.

Seles said: "She was just better today than I was. She really deserved it. I mean, a couple of shots she really got back. Like in the match point, it took courage to hit a ball like that. She was right on the line."

Garrison's goal is to transcend her role as a dangerous opponent and become a consistent champion, possibly even a major one. She has lacked a follow-up, rarely able to return a day after an upset to accomplish another. Whether Garrison can find it in the semifinals against Graf is doubtful, but then so was today's victory.