LOS ANGELES -- Two racket tosses and one anguished yell later, fourth-seeded Andy Roddick defeated No. 7 Xavier Malisse of Belgium 6-4, 6-4 in Friday's quarterfinals at the Mercedes-Benz Cup.

Roddick's victory set up an All-American semifinal against Jan-Michael Gambill, a 7-5, 7-6 (5) winner over Germany's Nicolas Kiefer.

Gambill won his third tiebreaker of the week.

"If you win those tough tiebreakers, you'll start winning matches,'' said Gambill, a 25-year-old player who has been surpassed by countrymen like Roddick, James Blake and Jeff Morrison, the lone American man to reach the third round at Wimbledon this year.

Defending champion Andre Agassi outlasted fifth-seeded Gustavo Kuerten 7-6 (3), 3-6, 6-4 for the second consecutive year. In 2001, Agassi was a three-set winner over the Brazilian in the semifinals, and went on to beat Pete Sampras for the title.

Agassi will meet No. 8 Max Mirnyi of Belarus, who beat Michael Llodra of France 6-4, 7-6 (4).

Agassi, seeded second, rallied from 3-1 down to win the first-set tiebreaker, hitting a forehand winner off Kuerten's short service return.

"It was pretty much the same kind of match, a lot of intensity,'' said Kuerten, who won the first set last year in a tiebreaker. "Every time we play, we test each other so much. It's two guys who like to play, hit the ball hard and enjoy the moments.''

Kuerten broke Agassi twice to win the second set, and served two games at love. Kuerten held a 17-11 advantage in aces for the match.

The intensity level increased in the third. Agassi and Kuerten exchanged service games at love and were on serve until the seventh game.

Kuerten slid and nearly fell chasing a forehand to set up break point. Agassi smashed a winner off Kuerten's second serve, then let out a satisfied yell and pumped his fist as he took a 4-3 lead. It was the only time Kuerten was broken in the match.

"It was my biggest match this year,'' said Kuerten, who had hip surgery in February and was off for two months. "A match like this, you give it everything you can. I tried to fight to the end. I'm a little sad it ends today.''

Kuerten survived two match points and seven deuces to hold serve and trail 5-4.

But Agassi served two consecutive aces to set up his third match point, and won with a forehand volley off a short return.

"His intensity on the court is amazing,'' Kuerten said of Agassi. "From the first point to the end, he's focused and with so much energy. He's special to the game. He's like a genius on the court.''

Serena Williams, the world's top-ranked women's player, actor Matthew Perry and figure skater Katarina Witt were among the crowd of 7,115 jammed into stadium court for the nearly two-hour match.

"This is as good a crowd as you could hope for,'' Agassi said. "They were rockin' tonight.''

Roddick, 19, improved to 4-0 in his career against Malisse, a semifinalist at Wimbledon.

Roddick broke Malisse's serve to open the hour-long match at the Los Angeles Tennis Center on the UCLA campus, and broke again for a 4-1 lead.

"I started out pretty fast and played just as well on the break points as I did the rest of the match,'' Roddick said.

Malisse broke back in the sixth game, when Roddick bounced his racket off the hard court for the first time. But Roddick served a love-game to wrap up the first set.

"My confidence doesn't waver too much,'' said Roddick, who had six aces to Malisse's nine. "I believe in myself and the weapons I have.''

Both players were on serve until Roddick broke Malisse in the seventh game of the second set. Roddick let loose with a loud yell after netting a service return to give Malisse a 40-30 lead. But the 22-year-old Belgian committed three consecutive errors to lose the game, and Roddick took a 4-3 lead.

The American won two of the final three games and advanced to his seventh semifinal this year. Roddick has won titles in Memphis and Houston in his second year on the ATP Tour.

"I'm learning on an everyday basis,'' he said.

Roddick created a stir in his rookie season, finishing the year as the youngest player in the top 20. He was the first American teenager to win three or more titles in a season since Pete Sampras won four in 1990.

"Last year, they didn't want to lose to an 18-year-old that they'd never really heard of. This year, they're trying to beat a top-15 player,'' he said of his opponents.

"Last year, everything I went to was new for me and it was new for everybody else seeing me. There was a lot of buzz and there was a lot of excitement around it. This year, getting to the semis here, it's kind of like, 'OK, whatever.'''