Tommy Haas withdraws; Juan Monaco in Duesseldorf semifinals

Qualifier Guido Pella of Argentina mastered cold and damp conditions to reach his first semifinal match on the ATP Tour by beating seventh-seeded Viktor

Tommy Haas' best finish at the French Open was a fourth-round appearance in 2002 :: Caroline Seidel/EPA

Qualifier Guido Pella of Argentina mastered cold and damp conditions to reach his first semifinal match on the ATP Tour by beating seventh-seeded Viktor Troicki 7-6 (5), 7-5 in the Power Horse Cup on Thursday.

A day earlier, Pella had beaten another Serb, top-seeded Janko Tipsarevic.

The 101th-ranked Pella next plays third-seeded Juan Monaco in an all-Argentine semifinal. Monaco defeated Tobias Kamke 6-3, 6-4 to improve to a 4-0 head-to-head against the German. Monaco is the highest seeded player left in the clay-court tournament, a warmup for the French Open that starts Sunday.

"It wasn't easy to play, as it was very cold," Monaco said. "I am happy to have reached the semifinals and I will have a difficult match against a baseliner tomorrow."

Sixth-seeded Jarkko Nieminen of Finland will meet Igor Sijsling of the Netherlands in the other semifinal on Friday. Nieminen advanced when second-seeded Tommy Haas of Germany withdrew with a cold.

"It makes no sense to come out and hit a few balls if I can't give my best," Haas said when he came out to address the crowd and explain his reasons for dropping out.

Sijsling also reached his first semifinal with a 6-3, 6-1 victory over Jan Hajek of the Czech Republic.