HAMBURG, Germany (AP) _ Gustavo Kuerten, the French Open champion, double-faulted on his match point and blew another in losing 4-6, 7-6 (10-8) 6-4 to Alex Corretja in the quarterfinals of the German Open Friday.

Kuerten, a Brazilian, dominated the first set with tremendous ground strokes and sudden changes of pace. But Corretja, a tenacious Spaniard who had two tough three-set matches Thursday, fought back.

Sixth-seeded Karol Kucera overcame a slow start to reach the semifinals with a 6-3, 6-2 victory over Austrian Thomas Muster, the 1995 French Open champion.

``I lost my concentration in the middle of the first set, I didn't attack the ball enough,'' Muster said.

The turning point came in the sixth game, when the two players exchanged a spectacular rally of diagonal drop shots. The rally ended with Muster hitting the net, Kucera went on to break Muster's serve and Muster never got back into the match.

``Once he takes over, he can put a lot of pressure on you and wrong-foot you,'' Muster said. ``He played a lot of top spin and kept me far behind the baseline.''

Kucera's semifinal opponent will be Albert Costa of Spain, who beat Fabrice Santoro 6-3, 6-4.

Costa, who was once as high as No. 9 in the ATP rankings, has fallen to No. 26 and is in his first semifinal of the year. He has won six tournaments, all on clay.

Felix Mantilla, another of Spain's clay court specialists, made the semifinals with a 6-0, 6-2 victory over an ailing Goran Ivanisevic of Croatia.

The $2.45 million tournament is a major tuneup for the French Open, the second Grand Slam event of the year that begins May 25.

Kucera said he is ready

``I wouldn't say I am one of the favorites, but if I am fit enough and I keep playing this well, I could win the French Open,'' the Slovak said.