Han shot a 5-under 67 in the final round, completing the first-ever LPGA event in Thailand at 14-under-par 202 for a five-shot victory over Diana D'Alessio.
It was a surprisingly commanding win for Han, who trailed second-round leader Nicole Castrale by two shots overnight. The first eight holes on Sunday decided everything, with Han collecting five birdies during that stretch while Castrale stumbled to three bogeys.
Castrale closed with a 3-over 75 to share third place with Candie Kung (69) and Gloria Park (71) at 8-under 208.
The trio ended one shot behind D'Alessio, who had a 2-under 70 to take solo second place at 9-under 207. D'Alessio got off to a poor start, but had three birdies on her back nine.
Han, who won the LPGA Corning Classic in May, was the only player to shoot three sub-70 rounds this weekend at Amata Spring Country Club.
Sunday, she posted her first birdie at the second hole, then four straight from the fourth. Han bogeyed the ninth and made the turn at 13 under.
On the back nine, Han got as low as 15-under after birdies at the 11th and 14th. Cruising at that point, she then finished her round bogey-birdie-bogey.
Her birdie at the 17th was her second this week at the 145-yard par-3, Asia's only true island green.
Han claimed $195,000 for the win and moved into eighth on the LPGA Tour money list with more than $1.11 million.
World No. 4 Cristie Kerr, the highest-ranked player in the field, shot a 2-under 70 and shared sixth place with Carin Koch (68), Brittany Lang (70) and Christina Kim (73) at 7-under 209.
Young Kim (69) and Sherri Turner (71) were one shot further back at 210.