KEY BISCAYNE, Fla. (AP) -- Martina Hingis handed Monica Seles the worst loss of her career today, 6-0, 6-0 in the semifinals of the Ericsson Open.

Seles, seeded seventh, won just 22 points and lasted only 39 minutes against the top-seeded Hingis. There were scattered boos from the crowd when Seles double-faulted on the final two points.

The defeat was just the third in 16 matches for Seles since she returned after being sidelined five months with a stress fracture in her right foot. Her worst previous loss was 6-0, 6-1 to Steffi Graf at Wimbledon in 1989.

Second-seeded Lindsay Davenport and No. 12 Sandrine Testud play in the other semifinal tonight. Hingis has lost five consecutive matches to Davenport, including two finals this year.

Two hours into his opening match at the Ericsson, little Lleyton Hewitt slammed a winner and waved his fist at the crowd.

``I want this match!'' he screamed.

Hewitt wants them all, and lately he has been difficult to deny. The 19-year-old Australian is the hottest player on the ATP Tour, and he'll face American Jan-Michael Gambill in tonight's men's quarterfinals.

The showing is Hewitt's best yet in the tour's Masters Series, but he's been winning all year.

He opened 2000 with tournament titles in Sydney and his hometown of Adelaide, reached the fourth round at the Australian Open, won two Davis Cup matches against Switzerland and then won the Scottsdale title.

He arrived at Key Biscayne seeded 14th, and his record for the year is 24-2 -- a lot of W's for a guy whose name starts with two L's.

``I got that winning feeling, and I didn't want to let it go,'' he said. ``That's the way it has been the past three months.''

The unseeded Gambill is a more unlikely quarterfinalist. He came to Key Biscayne with a 4-8 but has beaten three top-30 players -- Karim Alami, Magnus Norman and Aussie Mark Philippoussis.

One semifinal Friday is already set, with top-seeded Andre Agassi to face No. 6 Gustavo Kuerten. Agassi overcame four match points in a sloppy but thrilling tiebreaker Wednesday to edge No. 10 Tim Henman 7-5, 1-6, 7-6 (10).

``To win a match like that, you feel kind of proud,'' Agassi said.

Henman, rushing to the net at every opportunity, was one point from an upset victory at 6-5, 8-7, 9-8 and 10-9 in the tiebreaker. He served once with a match point and squandered that chance by double-faulting into the bottom of the net.

``It wasn't the ideal time,'' Henman said. ``But that's the way it goes.''

Kuerten beat unseeded Wayne Ferreira 6-3, 6-1.

The Hewitt-Gambill match shapes up as a baseline slugfest -- just the sort of challenge the Aussie likes. At 5-foot-11 and 145 pounds, Hewitt plays with a fury more common to Australian Rules Football, his sport until age 13.

His best shot is a service return that reminds some of Agassi.

``I think I was lucky enough to be born with it,'' Hewitt said. ``I used to play against 18-year-old when I was 12 or 13. I'd be trying to return their serve, and I'd never step back from the challenge. I was seeing a lot of big servers. They weren't big compared to the tour, but they were pretty big to me.''

Some opponents find Hewitt's style abrasive. Before a Davis Cup match last year between Australia and Russia, Yevgeny Kafelnikov said he was going to teach the youngster a lesson.

Hewitt beat Kafelnikov to clinch the round for the Aussies, then pretended to reach in his pocket for his wallet after the match.

``How much does he charge for a lesson?'' Hewitt asked with a grin.