Mika Miyazato, who is not related to fellow Japanese star Ai Miyazato, won by two strokes from Brittany Lincicome and Inbee Park.
She is the third Japanese to win the event after Ayaka Okamoto in 1986 and Ai Miyazato in 2010.
"It is very fulfilling for me to win along with those other famous players," Mika Miyazato said. "It was my dream to win and play on the LPGA Tour."
Her previous best finishes were second-place ties in the NW Arkansas Championship and LPGA Championship.
She finished on 13-under after recording a 2-under 70 in the third and final round. She led by two shots at the start of the day.
"At the beginning of the season, my short game was no good. I try to work more on short game," she said. "My golf game is getting better: I have more confidence."
After taking a three-stroke lead into the back nine, she bogeyed the 10th to find herself just a stroke ahead of four players.
The key hole was the par-3 11th, where a tee shot seemingly destined for the creek hit a rock and bounced near the green. A 25-foot putt saw her par the hole.
"My tee shot - I thought I got it into the water hazard," she said. "Maybe lucky for me there."
American Lincicome moved up the leaderboard with a final-round 67, while South Korea's Park, who was tied third before the round, recorded a 69.
Cristie Kerr had been level with Park but shot a 70 to finish the event tied for fourth with So Yeon Ryu (71) and Korean Haeji Kang, whose 66 was the best round of the day.
Michelle Wie had her first top-10 finish of the season, a 69 placing her eighth at 8-under.
"It feels good to get on the leaderboard and see my name up there consistently this week," Wie said. "It was a lot of fun."
- Sports & Recreation
- Mika Miyazato
- Brittany Lincicome