Also today, second seed Sebastian Rieschick, of Germany, defeated the top-seeded Australian Brydan Klein 7-5 6-3 in the final of the $US15,000 ($NZ19,314) men's Futures tournament.
While there was plenty of good shot making in the men's final, it was the women's match which had the intensity as both Kostova, ranked No 255 in the world, and Sema, ranked 14 places above her, stared each other down after points and screeched louder as the match became closer and the score see-sawed.
Eventually it was Sema who prevailed to add to her two wins and one runner-up placing in her last four events.
Sema hit a nagging length on most of her shots and refused to let the flair of Kostova put her off her own game.
Rieschick beat Klein in a final for the second time in a week, having won at Esperance in Western Australia last weekend.
Klein now has four successive runner-up finishes while the German notched his fourth Futures title of the year.
