Thailand's Pornanong Phatlum shot a six-under 67 to hold onto her first-round lead and win the LPGA Brasil Cup by four shots.
Phatlum went into the final round of the two-day tournament at Itanhanga Golf Club in Rio de Janeiro tied with France's Karine Icher on seven-under.
The 22-year-old from Thailand backed up her impressive opening day with a strong start to Sunday's round.
Phatlum hit five birdies on the front nine, including consecutive birdies on the seventh, eighth and ninth holes.
Another birdie on the 11th and no dropped shots, allowed Phatlum to win her first ever tournament on the LPGA Tour.
Taiwan's Amy Hung shot the best round on Sunday, an eight-under 65, to finish second.
Hung finished a shot ahead of Paula Creamer and Chella Choi (both eight-under), with Amanda Blumenherst, Brittany Lang, Candie Kung, Katie Futcher and Icher all on seven-under.