Petrova rolled to a 6-2, 6-1 victory in a match that lasted just over 70 minutes.
The win gave Petrova her first championship this year and eighth on the WTA tour. Dechy played in her first title match.
"I expected a much more difficult match today," Petrova said. "I served well and hung in the rallies well. I was very focused today. I knew I had to play very clean and not give her any chances."
The Ohio hard-court event is considered a tuneup for the U.S. Open, which starts Aug. 25.