Tsitsipas was close to going down an early break in the decider as he faced three break points, but his serve was able to bail him out of trouble.
"I fought very hard and gave my soul out on the court, which is the biggest pleasure in this sport," Tsitsipas said.
The 20-year-old is going for his second title of the season, third overall. In January, he made a Grand Slam breakthrough by reaching the Australian Open semifinals, taking out Roger Federer in the fourth round en route.
Earlier on Saturday, the Greek's compatriot Maria Sakkari defeated Johanna Konta in the Rabat final for her maiden career WTA title.
Up next for Tsitsipas is either Pablo Cuevas or Alejandro Davidovich Fokina.