The 24-year-old Thiem, ranked No. 6 in the world, didn't lose a set in the clay-court event. He won his ninth career title and first since an event in Rio de Janeiro in February 2017.
"When you win a tournament, it's good news because we're used to losing more than winning," Thiem said. "With these conditions -- slow and hot -- there are many chances for me to play well. It was my goal before starting the week, and it is incredible to have achieved it."
The 24-year-old Bedene dropped to 0-3 against Thiem.