Green went into the final day with a two-shot advantage, but Boutier hit five birdies in her final seven holes to card a six-under 66 and lead in the clubhouse on 18-under par at Seowon Valley Country Club.
Green's birdie on the 17th hole proved enough to clinch her third title of the year, as she finished with a round of 71 and a 19-under par total of 269.
"It helps that I've been hitting the ball well, and when the putter goes well, it does go well," said the 27-year-old.
"So just making sure that I can stay consistent.
"But I still have four or five more tournaments for the rest of the year, so I want to continue to work hard and have myself in these type of positions."
It was the sixth LPGA title for Green, who won a major at the 2019 Women's PGA Championship.
The 30-year-old Boutier, who finished in a share of ninth at last week's LPGA Shanghai, said: "I had a lot of opportunities on the front (nine) but I just wasn't able to convert.
"And on the back, I was able to hit a few really close and that gave me kind of confidence."
Thailand's Channettee Wannasaen also put herself into title contention with a four-under-par final round.
The 20-year-old hit four birdies and an eagle on the front nine to go top of the leaderboard, only for her challenge to fizzle out with two bogeys on the back nine.
Olympic champion Lydia Ko finished six strokes off the pace on 13-under par.
The New Zealander was close to the leading pack heading into the weekend but fell behind after carding a 71 on both of the final two days.
Defending champion Minjee Lee of Australia finished tied 33rd on five-under par after a disastrous five-over par 77 in her final round
