In pounding the defending champion, the second-seeded Radwanska, 19, captured her third career singles title on the women's tennis tour and second this season.
She maintained a perfect record in finals (3-0) after winning the Nordic Light Open in Stockholm, Sweden last August and the Pattaya Women's Open in Pattaya City, Thailand, in February.
Saturday's victory was worth $30,500.
"I was nervous in the beginning, but I woke up and tried to play my game," Radwanska said after she became the sixth player in 2008 to win multiple singles titles.
Dementieva, the top seed, was trying for her 10th career singles title and second this season.
She won the Dubai (United Arab Emirates) Tennis Championships in February.