Hsu took two hours and 45 minutes to subdue a fighting Vaishnavi 6-4 4-6 7-6(5) to claim her third singles title of the year.
She had earlier won similar events in Japan and Dehradun.
"It was a tough match and Vaishnavi served very well. It was too close a match," 19-year-old Hsu said after the match.
However, it was heart-break for Vaishnavi, who made it to her first final after September last year.
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In the first set, Hsu stuck to the baseline and occasionally rushed to the net to confuse her opponent and secured a break in the 9th game, which was enough for her to win the set.
In the second set, Vaishnavi found her rhythm and served fluently and broke Hsu in the 10th game to force the deciding final set.
Vaishnavi held on to her serve and led 5-4 and then was two points away from victory as she hustled Hsu into committing errors.
Later in the tie-break, Hsu looked stronger and wrapped up the match and the title on the first match point.
While Hsu got Rs 99,250 and 12 WTA points, Vaishnavi pocketed Rs 62,000 and seven WTA points.