Swede Madelene Sagstrom won the Gainbridge LPGA title at Rio Boca on Sunday when Nasa Hataoka missed a three-foot putt at the final hole in Boca Raton, Florida.
Sagstrom expected a play-off after sinking a testing six-footer for par before watching on with surprise as the Japanese hit a weak putt that dribbled right of the hole.
The Swede initially looked shocked and reluctant to celebrate, before finally breaking into a big smile and hugging her caddie.
"I just told myself keep fighting. It will happen if it's meant to happen, and it did," Sagstrom said on clinching her first LPGA Tour victory at the age of 27.
With a two-under-par 70, she became the 12th Swede to win on the LPGA Tour.
Sagstrom finished at 17-under 271, while Hataoka (69) was second on 16-under.
Northern Ireland's Stephanie Meadow finished in a tie for 35th on two-under after carding her worst score of the tournament, a three-over-par 75. It was a disappointing end for Meadow, who'd sparkled on Saturday with a four-under 68.
Leona Maguire missed the cut on Friday.
The LPGA Tour will take a one-week break before a five-tournament swing in Australia, Thailand, Singapore and China.