Kris Tamulis, a 10-year LPGA veteran, rallied from three shots back on Sunday to lift her first tour title at the Yokohama Tire LPGA Classic.
The American fired eight birdies in a seven-under par 65, her 17-under total of 271 giving her a one-stroke victory over former world number one Tseng Ya-ni and third-round leader Austin Ernst.
"My swing felt really good," Tamulis said. "I`ve really been working hard on my putting the last couple weeks.
"These greens are probably the fastest I`ve played in I don`t even know how long," she added of the Senator course playing surfaces that were barely slowed by Saturday`s rain.
"So I`ve been just working on the speed and trying to hit it on the right side of the hole."
After weather delays totalling more than five hours on Saturday, players faced a marathon final day.
Tamulis played 29-holes, getting on a roll with a third-round 67 on Sunday morning.
With all the holes of the long day running together, Tamulis said she didn`t even realize she had gone so low in the final round.
"I didn`t even know that I shot seven-under until I counted my birdies and then subtracted my bogey," she said. "We were trying to beat the weather all day and I think we were really lucky that we finished today."
Ernst had stretched her lead over Tseng to two strokes heading into the final round, but finished with a three-under par 69 for 272.
Tseng`s quest for her first victory since 2012 was undone by two bogeys in a final round that also included seven birdies.
Her five-under 67 still gave the Taiwanese star her best finish since a tie for second at the LPGA Thailand in February.
Americans Sydnee Michaels (67) and Lexi Thompson (69) shared fourth place on 274, two strokes in front of Americans Stacy Lewis and Jaye Marie Green.