"A title is the best, it's the best thing you can have in tennis. A big one or a small one, it doesn't matter," said Garcia, who clinched her fourth career title.
The 20th-ranked Garcia, playing her first final of 2017, struck first by breaking Barty's serve in the seventh game and holding the next to take a 5-3 lead. Barty easily held her serve and broke back for 5-5. Neither player could then hold their serve and Barty won the tiebreaker.
The second set saw both players struggling for consistency in their serves and trading breaks. Barty's sliced backhand caused her Australian opponent some problems and she served twice for the set but was unable to close. It was Garcia's turn to win the tiebreaker.
Garcia went 3-1 up in the decider and gained another break before taking the title with a stunning serve.
"I feel this where I belong," said 37th-ranked Barty, who beat French Open champion Jelena Ostapenko in the semifinals. "I've had a fantastic year so far."