Martin defeated Rochus for the fourth straight time, 6-3, 6-2, on a hot, humid day along the Croatian coast.
Local wild card Ivo Karlovic will be Martin's next opponent after the 6-10 Croatian beat Rochus' older brother, Christophe, 7-5, 6-4. Karlovic shot to prominence at Wimbledon last month when he dethroned defending champion Lleyton Hewitt.
Karlovic is playing his first tour event since losing to Max Mirnyi in the third round at the All England Club.
Slovakian Dominik Hrbaty crushed fifth seed Fernando Vicente, 6-3, 6-0.
The tournament lost another seeded player as No. 3 Felix Mantilla withdrew due to a viral infection. Croatian Sasa Tuksar took Mantilla's place.
Mario Radic beat Italian Giorgio Galimberti, 1-6, 6-4, 6-4.