Despite carding a one-over-par 73, Haru Nomura won the Swinging Skirts LPGA classic in San Francisco by four strokes.
Nomura, who will now be one of the LPGA favourites next time she tees off, ended the tournament on nine-under and finished ahead of South Africa's Lee-Ann Pace, who came second on five-under.
Gerina Piller and Na Yeon Choi finished in a tie for third on four-under, while world number one Lydia Ko was in a tie for sixth on one-under.
Nomura struggled on the front nine and was in danger of blowing her lead after carding a hat-trick of bogeys from the seventh to ninth as it left Na Yeon Choi trailing by one shot.
However, the 23-year-old converted a mammoth 70-foot birdie putt at the 12th to settle any nerves before going on to make birdies at the 14th and 17th, which ensured that she captured her second title of the year after winning the Australian Women's Open in February.
Pace was in all sorts of trouble at the beginning of her round of 74 as she began with five consecutive bogeys from the first to fifth. She rounded off the front nine with birdies at the sixth and ninth before proceeding to have a more successful back nine, where she made three birdies and two bogeys.
Choi, who fired a 75, only made two bogeys on her front nine, but seemed to be finding her touch at the beginning of the back nine as she made a duo of birdies. However, a bogey at the 15th and a double bogey at the par-four 16th sullied her round and put her out of contention.
Piller recorded a 73 on Sunday and enjoyed a successful front nine as she made two birdies, but double bogey at the par-four 11th and a bogey at the 13th didn't help her cause.
Meanwhile, Ko, who carded a 75, had a disastrous front nine as she made four bogeys on her first seven holes. The world number one never recovered after her horror start as she only made one birdie on the back nine.
Ko will not be at next week's LPGA Texas Shootout, making things interesting from a golf betting perspective.
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The Northern Irishman shot seven-under 63.