Umag, Croatia -- (Sports Network) - Second-seeded Croat Ivo Karlovic lost his second-round match Thursday, while fifth-seeded Croat Ivan Ljubicic pulled out at the clay-court Croatia Open Umag.

Argentine Maximo Gonzalez upended the 6-foot-10 Karlovic 3-6, 6-3, 6-4, while Croatia's Roko Karanusic advanced via walkover when Ljubicic decided against playing on Day 4 due to a back injury, at ITC Stella Maris.

Fourth-seeded Russian Igor Andreev advanced in straight sets over Spain's Daniel Gimeno-Traver 6-2, 7-6 (7-3).

Meanwhile, sixth-seeded Argentine Guillermo Canas snuck into the quarters by outlasting Serbian Boris Pashanski 6-7 (3-7), 6-3, 7-5 after almost three hours of tennis. Canas captured this championship four years ago.

Friday's quarterfinals will pit top-seeded Spaniard Fernando Verdasco against German Mischa Zverev, third-seeded Spaniard Carlos Moya versus seventh-seeded Italian Fabio Fognini, Andreev will face Canas, and Karanusic against the upstart Gonzalez. The five-time Umag titlist Moya beat Romanian Andrei Pavel in last year's finale, also titled here in 1996 and from 2001-03, and was the runner-up in 2005.

The 2008 Umag champion will collect $86,000.