The 29-year-old Scot beat Kana Nagai by four strokes for her first LPGA Tour title, while overnight leader Momoko Ueda tied for fifth at 12-under 276.
The two-time winner of the tournament birdied the final hole of the third round to remain on top. Gemma Dryburgh is one shot off the pace.
The 2007 and 2011 tournament winner has a one-stroke advantage over compatriots Ai Suzuki and Miyuu Yamashita.
Ai Suzuki, the 2019 tournament champion, and Momoko Ueda carded 7-under 65s to finish one stroke ahead of compatriots Ayaka Furue and Sakura Koiwai.
The Kobe native finished two shots off the pace after entering the final round in a three-way tie for the tournament lead in Portland, Oregon.
The 22-year-old Kobe native captured her first LPGA Tour title with a career-best round in a come-from-behind victory.
Hataoka, who finished at 15-under 269, was the only golfer to score in the 60s in all four rounds at Wilshire Country Club.
The Swallows third baseman and Buffaloes hurler received top vote totals in the Central League and Pacific League, respectively.
The 22-year-old Ibaraki Prefecture native earns her first title on the LPGA Tour since March 2019.
Saso, who was born in the Philippines, defeated Nasa Hataoka in a three-hole playoff to become the second teenager to win the golf major.