The 22-year-old Berrettini snatched the opening set tiebreak 11-9, before converting a break point in the 10th game of the second to wrap up the victory.
"From the beginning until the end it was really tough to break him," Berrettini said. "I served really good most of the days and it was an unbelievable tiebreak.
"If I lost the tiebreak, I think the match would have been really tough. I was lucky I did a really good job."
Playing in his first tour level final, Berrettini produced a fearless display, firing 17 aces and losing 12 points on serve in total.
He finished the tournament without dropping a set, ousting 2016 champion Feliciano Lopez and fourth seed Andrey Rublev on his way to lifting the title.
(Reporting by Hardik Vyas in Bengaluru; Editing by Christian Radnedge)
