A closing round 73 saw Leona Maguire finish on level par at the BMW Ladies Championship in Busan, 22 shots adrift of winner Ko Jin-young.
The Cavan woman was one-under for the opening nine holes, but on a day of high scoring, three bogeys on the back nine saw her slip further down the leadeboard.
World number two Ko Jin-young staved off a spirited challenge from Lim Hee-jeong on Sunday to seal a dramatic play-off victory and become the 200th South Korean champion on the LPGA Tour.
Ko set the LPGA International Busan course alight with an eight-under-par 64 in the final round that had eight birdies, including one in the 17th, to grab a share of top spot.
But Lim made a par on 18 to stay level at 22-under overall, forcing a playoff.
The 26-year-old Ko made another gain in the first playoff hole - the par-four 18th - after a superb approach shot and overnight leader Lim could only manage a par to hand the championship to her compatriot.
The victory is the 11th of Ko's career and follows her wins in the Volunteers of America Classic, the Cambia Portland Classic and the 2021 Cognizant Founders Cup this year.
She is projected to become the top-ranked women's golfer in the world replacing American Nelly Korda.
It was a disappointing finish for the 21-year-old Lim who came into the final round of the $2 million event on the back of a course record 198 after 54 holes.
Ko, who was second after three rounds, briefly claimed the outright lead following the 12th hole when she sank a 10-foot putt and was neck-and-neck with Lim for much of the day.
Having fired six birdies on the front nine, she raised her game after a brief dip to complete the par-four 17th hole in three shots to improve her title hopes.
Ko's composure made all the difference in the sudden-death scenario as Lim was unable to force a second playoff hole.