Yin ran in a 25-foot birdie putt on the par-5 12th for a share of the lead with South Korean playing partner Kim.
The 23-year-old parred the next five holes in breezy conditions and birdied the par-five 18th for a two-under 70 and a two-stroke victory.
"I think this one definitely boost my confidence a little bit," Yin said.
"I just want to enjoy the moment."
Kim shot 71. She dropped back with a three-putt bogey on the par-three 16th, missing a nine-foot par try. The South Korean player — a two-time winner this season — missed a seven-foot birdie attempt on the par-three 17th.
"At the end of the day it was Ronni," Kim said.
Karis Davidson was the highest-placed Australia player in a group of four players tied for 17th.
Sei Young Kim chipped in for birdie on the par-three 11th to take a one-stroke lead in the final group, then dropped four shots on the next three holes with a double bogey and two bogeys. She shot 73 to tie for fourth.
Yin won twice in 2023 and three times in 2024, with a span of 672 days since her last win in the 2024 Maybank Championship.
"It's just been so long since my last win," Yin said
"I know I work hard and also my team, my mom is here. Just everything comes together."
Allisen Corpuz was third at 11 under after a 68. Fellow US Solheim Cup player Rose Zhang (68) was another shot back with Sei Young Kim.
Top-ranked Nelly Korda tied for 50th at one over after a 73 in the final event before September's Solheim Cup matches in the Netherlands.
European captain Anna Nordqvist finished her final final event on the LPGA Tour in tie for 38th, ending on one under after a 72.
"I'm not really sure how to feel," Nordqvist said.
"Nothing ever prepares you for this moment. I'm definitely going to miss it.
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