Cilic, the world's 13th-ranked men's player, beat fourth-seeded Philipp Kohlschreiber of Germany 6-4, 7-6 (7-4), despite Kohlschreiber saving 6-of-8 break points in the 98-minute match.
"I came here with the mind to play well," Cilic said. "I'm really pleased I kept my form on a good level (and) played four very good matches."
His opponent in Sunday's final, the seventh-seeded Melzer, was a 4-6, 7-6 (7-5), 6-4 comeback winner over unseeded Janko Tipsarevic of Serbia.
"After winning the second set in a very close tie-break, I felt like I had the momentum on my side and I was playing pretty well," Melzer said.
He hit 17 service aces and saved 3-of-4 break points.
Melzer has a 1-6 record in career finals.