Kim Sei Young chipped in for par to force a playoff then holed a shot for eagle to beat Park In-Bee in the LPGA LOTTE Championship.
Kim, who took a one-shot lead into the final round on Saturday, closed with a one-over par 73 for 11-under 277.
She was joined there by world number three Park, who posted a one-under 71 in the final round.
Kim, who won her first LPGA title in her second start as a tour member at the Pure Silk-Bahamas in February, saw her chances of nabbing a second trophy dwindle after her drive at the 72nd hole bounced and ran through the fairway and into the water.
After taking a drop, she missed the green left with her third shot.
Meanwhile Park, playing from the rough just short of the water, hit her second shot some 60 feet from the hole. She lagged her birdie putt within inches of the cup and marked her ball.
Then Kim holed her chip for par to force the playoff.
“I tried to only focus on getting the ball to the hole because I didn’t have (much) of a chance,” Kim said.
They returned to the 18th tee for the playoff and both Kim and Park hit shorter tee shots.
Kim barely cleared the water with her second shot — from 154 yards out with an eight-iron — but her ball bounced and landed in the hole for eagle.
“I don’t believe what happened there,” said Kim, whose crown was secure after Park left her approach short. “It’s still unbelievable.”
The 22-year-old became the first player this year to win two LPGA titles.
South Korea’s Kim In-Kyung bogeyed the last two holes in a two-over 74, finishing alone in third on nine-under 279.
South Koreans Kim Hyo Joo (69) and Chella Choi (72) shared fourth on 281.
Defending champion Michelle Wie closed with her second straight 73 to finish in a tie for 11th.
The LPGA Tour heads to California next week for the Swinging Skirts LPGA Classic, where world number one Lydia Ko of New Zealand will defend her title.