Dusseldorf - Qualifier Guido Pella of Argentina advanced to his first semi-final 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 plays third-seeded Juan Monaco in an all-Argentine semi-final. Monaco defeated Tobias Kamke 6-3, 6-4. Monaco is the highest seeded player left in the clay-court tournament, a warmup for the French Open.
Sixth-seeded Jarkko Nieminen of Finland will meet Igor Sijsling of the Netherlands in the other semi-final on Friday. Nieminen advanced when second-seeded Tommy Haas of Germany withdrew with a cold.
Sijsling reached his first semi-final with a 6-3, 6-1 victory over Jan Hajek of the Czech Republic.
Results from the fifth day of the Dusseldorf ATP tournament (x denotes seeding):
Guido Pella (ARG) bt Viktor Troicki (SRB x7) 7-6 (7/5), 7-5
Juan Monaco (ARG x3) bt Tobias Kamke (GER) 6-3, 6-4
Igor Sijsling (NED) bt Jan Hajek (CZE) 6-3, 6-1
Jarkko Nieminen (FIN x6) bt Tommy Haas (GER x2) - walkover