South Korea's Ahn Sun-ju shot an even-par 72 on Sunday to seize a one-stroke victory at the Yamaha Ladies.
Ahn, the leading money winner on Japan's LPGA tour in 2010 and 2011, started the day a stroke back of overnight leader Yumiko Yoshida. Ahn carded one birdie against a lone bogey to earn her first victory of the season with a total of 5-under-par 283.
"I was resigned to finishing this in a playoff," Ahn said. "I felt that if I could just play patient golf, I would come out as the winner.
"I wasn't able to play my usual aggressive style of golf here, so I want to be able to do that next time."
Yoshida blotted her scorecard with a pair of bogeys to settle for second, while the trio of Erina Hara, Yukari Baba and Ritsuko Ryu tied for third two strokes further back at Katsuragi Golf Club.
Last year's top money winner, Rikako Morita, finished at 1-over par for the weekend in a tie for eighth place.
Ahn is currently second in this season's tour money rankings behind Thailand's O. Sattaya.