The victory made the 19-year-old the first LPGA player in five years to win twice in her rookie season.

Overnight leader Thitikul shot a closing three-under 68 while American Kang roared home with a 64 as they finished the 54 holes of regulation at the Pinnacle Country Club tied at 17-under.

“I didn’t see a leaderboard until 18,” Thitikul said. “I thought a par would be good enough.”

The two matched pars on hole No.15, the first sudden-death hole, and then Thitikul made a birdie putt on No.16 to win.

Chella Choi of South Korea finished third, a shot behind the leaders.

Australian youngsters Steph Kyriacou (68) and Karis Davidson (71) tied for 39th at seven-under.

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Thitikul had won the JTBC Classic earlier in the season, also in a play-off.

“On the second hole play-off, I had a chance to make a birdie, because it was not that far. Then, in my mind, I just told myself, ‘Do your best, even it's not going in. Just do the best you can’,” Thitikul said.

The $US345,000 first-place cheque pushed her earnings to $US1,881,392 for the season. She has made 19 cuts in 20 events and added nine additional top-10s, including a solo fourth at the KPMG Women's PGA Championship.

Thitikul became the fourth player with multiple victories this season, joining Jennifer Kupcho (3), Minjee Lee (2) and Brooke Henderson (2).

A six-time winner on the LPGA Tour, Kang was making her third Tour start since June after undergoing treatment for a tumour on her spine.

"It's emotional," said Kang. "I'm just really proud that I'm even here. So obviously I wanted to win, but these are like tears of joy."