Second-seeded Cilic completed a run through the Umag event without losing a set, besting Granollers 6-4, 6-2 in the championship tilt.
Cilic, 23, won his second final in two months. He racked up his first career title last month on the grass courts of the Queen's Club in London.
Granollers, meanwhile, fell to 1-5 lifetime against the Croatian.
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