In his first Croatian Open appearance, Verdasco qualified for a semifinal for the third time in his last four events.
Fellow Spaniard Carlos Moya, a five-time Umag champion, was not as fortunate. Moya lost 6-4, 6-3 to No. 7 seed Fabio Fognini of Italy. With his win, Fognini, 21, reached a semifinal for the second time in his young career.
Fourth-seeded Igor Andreev of Russia topped sixth-seeded and former Umag winner Guillermo Canas of Argentina 7-5, 6-4; while Argentina's Maximo Gonzalez overcame Croatian crowd favorite Roko Karanusic 2-6, 6-3, 7-6 (7-4).
In Saturday's semis, Verdasco faces Fognini and Andreev meets Gonzalez.
Sunday's champion will collect $86,000.