Apparently, the secret to great tennis isn't a walloping serve or solid groundstrokes. The secret is being in love.

"When there is love, you are inspired -- you can write poems, you can write music, you can play good tennis, whatever," said Andrei Medvedev, who has recently rekindled his romance with fellow tennis player Anke Huber. "Imagine playing a miserable guy and a happy guy. Who is going to win?"

At the French Open today, the happy man prevailed, as Medvedev scored a major upset over Gustavo Kuerten of Brazil, 7-5, 6-4, 6-4. Kuerten had been seeded eighth, but was a favorite to win here after a stellar clay-court season. Medvedev, whose world ranking had plummeted from No. 4 in 1994 to No. 105 two months ago, wasn't even a favorite to win his second-round match last week, when he faced Pete Sampras.

But Medvedev defeated the world's No. 2 player in four sets, and today he advanced to the semifinals. He will face Brazilian Fernando Meligeni, who upset sixth-seeded Alex Corretja of Spain this afternoon, 6-2, 6-2, 6-0. Corretja, who has been ill, appeared worn out at the end of his match; Kuerten, who had no such excuse, simply looked stunned. But then again nearly everyone seemed shocked by Kuerten's loss except Medvedev, who looked comfortable in a pair of loose madras plaid shorts as he maneuvered toward the net for drop shot after drop shot.

"I am born again, a second life, I don't know what you want to call it," Medvedev said. "I don't think there is anyone happier on earth than me right now. It is a second birth in tennis, in life. I feel fantastic. It's difficult to describe with words, really."

Medvedev denied recent rumors that he and Huber, whom he had been dating sporadically for more than six years, are getting married. "If we will, you will all know in advance, so no excuses for no presents," he said. However, he was eager to expound on how happy Huber has made him.

"We were on and off a few times, and then there was a long spell when we were apart," he said. "I don't want to offend anybody I've been with before, but there is something special about Anke. Otherwise, we wouldn't be coming back to each other all the time."

Huber, the world's 30th-ranked women's player, had to withdraw from the French Open because of an injury but she likely will return to Paris to watch Medvedev play Meligeni in Friday's semifinals. Meligeni looked confident as he dispatched Correjta, last year's French Open runner-up, but Correjta did not offer much of a challenge. Corretja said after the match that the virus he has been battling prevented him from keeping up with Meligeni after five shots had been exchanged on any point.

"After five minutes, I already saw I was not able to play," he said. "I was feeling dead on the court, and my legs were very heavy. I thought maybe after the beginning I would get in shape, but I didn't. It was a pity."

Meligeni was pleased to be in his first Grand Slam semifinal, although he was not the Brazilian any of his peers expected to reach the tournament's final four. Kuerten was considered the heavy favorite in the locker room and in the local newspapers, and as he faced Medvedev's fourth match point today, he looked as if all that pressure had become too heavy to bear.

After Medvedev hit the winning shot -- a drop shot to the left side of the court that Kuerten slid toward in vain -- Kuerten whacked the ball into the stands in frustration.

"I think it's kind of a frustration because you are there, trying your best, but you are not feeling the ball well," Kuerten said. "He's a tough player, and he did many different shots, serve well, return pretty well too. So it was difficult."

Injuries and inconsistency had contributed to Medvedev's drop in the rankings over the years, but he said he has been working hard on his game for the past six weeks, which is about how long he has been seeing Huber again. He practiced for this tournament at home in Kiev, Ukraine, while many other players competed on Europe's clay-court circuit, but he watched several of the matches on television and became convinced he was ready to compete.

Defeating Sampras in the second round gave his confidence another major boost, even though Sampras's struggles at the French Open are well known. "Beating Pete -- well, it doesn't matter if it's on clay or mud or water," he said. "You beat him in backgammon, you feel good. With complete respect to Pete, beating him was an unbelievable lift for me. Now it's even more confidence than before. We'll see where it takes me."

French Open

When: Through Sunday.

Where: Roland Garros, Paris.

Defending Champions: Carlos Moya and Arantxa Sanchez-Vicario.

Today's TV: 8 a.m., USA.

Yesterday's Key Results: Men's Singles, Quarterfinals -- Andrei Medvedev, Ukraine, def. Gustavo Kuerten (8), Brazil, 7-5, 6-4, 6-4; Fernando Meligeni, Brazil, def. Alex Corretja (6), Spain, 6-2, 6-2, 6-0. Women's Doubles, Quarterfinals -- Martina Hingis, Switzerland, and Anna Kournikova (2), Russia, def. Larisa Neiland, Latvia, and Arantxa Sanchez-Vicario (7), Spain, 6-2, 6-3; Serena Williams and Venus Williams (9), Palm Beach Gardens, Fla., def. Els Callens, Belgium, and Rita Grande, Italy, 6-0, 7-5; Lindsay Davenport, Newport Beach, Calif., and Mary Pierce (12), France, def. Jana Novotna, Czech Republic, and Natasha Zvereva (1), Belarus, 2-3, retired; Alexandra Fusai and Nathalie Tauziat (4), France, def. Elena Likhovtseva, Russia, and Ai Sugiyama (5), Japan, 2-6, 6-4, 11-9.

Today's Featured Matches: Women's semifinals -- Hingis (1) vs. Sanchez-Vicario (7); Monica Seles (3) vs. Steffi Graf (6).

Remaining Women's Singles Schedule: Final, Saturday.

Remaining Men's Singles Schedule: Semifinals, Friday, Andre Agassi vs. Dominik Hrbaty; Meligeni vs. Medvedev. Final, Sunday.

CAPTION: Unseeded Andrei Medvedev reacts triumphantly to his 7-5, 6-4, 6-4 French Open quarterfinal win over eighth-seeded Gustavo Kuerten at Roland Garros.