The American had a three-round total of 21-under 195 at Siam Country Club's Pattaya Old Course.
Sponsor invite Akie Iwai of Japan, who led after the first two rounds, shot 71 and dropped into second place on Saturday.
The 22-year-old earned her LPGA tour membership after finishing in a tie for fifth at the LPGA Final Qualifier last year.
Yin's best finish in four previous appearances at LPGA Thailand was a share of third place in 2021.
"Off the tee, I wasn't hitting it as well as the last two days, but I got away with some good lies and managed to capitalize on my opportunities," said Yin, the 17th-ranked 26-year-old.
The California native is chasing her second LPGA title after winning the Buick LPGA Shanghai in 2023. She is a two-time major runner-up — at the 2023 Chevron Championship and the 2019 US Women's Open.
Local stars Moriya Jutanugarn and Jeeno Thitikul each posted a 69 to sit at 201, a stroke behind Iwai. Both are looking to improve their best home-soil results — Jutanugarn finished tied for second in 2018, while Thitikul was the lone runner-up in 2021.
World No.2 Jeeno Thitikul, who turned 22 on Thursday, shot 69, as did fellow Thai Moriya Jutanugarn to be joint-third at 15 under.
Defending champion Patty Tavatanakit (65) is 12 under, with 2023 winner Lilia Vu (74) of the United States seven over.
Gabriela Ruffels is the best-placed Australian in a tie for 39th at three under after her round of 72.
Steph Kyriacou (75) is two over, with Grace Kim (75) a further six shots adrift.
The event is the first stop of the LPGA's so-called Asian swing before the tour moves to Singapore and China over the next two weeks.
