Zabgeab - Lukas Lacko of Slovakia beat seventh-seeded Robin Haase of the Netherlands 6-4, 6-4 to reach the semifinals of the Zagreb Indoors on Friday.
Lacko, who earlier ousted second-seeded Alex Bogomolov Jr of Russia, will now face Marcos Baghdatis of Cyprus, who advanced after defeating defending champion Ivan Dodig of Croatia 6-4, 7-5.
"I am very much pleased with the way things work here," Lacko said. "I am looking forward to the semi-finals."
Sixth-seeded Baghdatis ousted the fourth-seeded Dodig with little trouble, leaving host country Croatia without representatives in the semi-finals or finals for the first time since 2006.
Germany's Michael Berrer also advanced after defeating Austria's Jurgen Melzer 5-7, 6-4, 6-4. Berrer - a finalist in 2010 and 2011 - rallied after failing to convert five break points in the first set.
"I just feel very comfortable here," Berrer said. "I had lot of respect for Melzer ... I knew it would be difficult and that I had to be on the top of my game to beat him."
Berrer will play against third-seeded Mikhail Youzhny of Russia, who defeated another, eighth-seeded Croat Ivo Karlovic 7-6 (12/10), 3-6, 7-6 (9/6).
"This one was really tough, I was lucky this time," Youzhny said. He converted the fourth match point as Karlovic netted a volley.
"When you lose the match, especially like this one, you don't feel well," Karlovic said. "But I played good game. I missed two important volleys ... and I lost the match because of these points."