After the two parred the par-3 16th, the championship was essentially decided on the par-5 17th, where Ryu picked up a birdie against Seo's bogey.

Seo's tee shot there landed on a right side bunker. She punched it out to the fairway, pushed her third shot to the right, and her pitch came up well short of the hole. The ensuing 20-foot par putt grazed the right lip of the cup.

Ryu stayed in the middle of the fairway with her first two shots and struck her third to about eight feet. She drained the putt for a birdie and a two-shot lead.

On the par-4 finishing hole, Ryu struck the final blow by landing her second shot within about five feet and making the birdie putt. Seo went long with her second, and two-putted for par.

The playoff was a deja vu of sorts for Seo and Ryu, who have battled each other for titles on the Korean tour. Ryu has seven Korean LPGA victories to her credit while Seo has 11 wins on that tour.

Inclement weather forced a Monday finish, and only three players finished below par for the tournament.

Seo had finished her tournament at three-under on Sunday, local time, before darkness suspended the rain-interrupted final round, and slept on a one-shot lead over Ryu. Seo had five birdies on the front nine, including four straight starting on par-4 sixth, and scrambled her way through the rest of the round to maintain the lead.

Ryu was at two-under with three holes to play when the final round resumed. She closed out her final round by slamming home a six-foot birdie putt on the 18th to force the playoff. After a 74 in the first round, she fired three straight rounds of 69.

Ryu is still a full-time member of the Korean tour. Seo won her first U.S. event last year as a non-LPGA member, and this is her first full LPGA season.

Defending champion Paula Creamer of the U.S. ended in a tie for 15th at six-over, along with world No. 1 Yani Tseng.

There were four other South Koreans in the top 10, including 2008 champion Park In-bee, who tied for sixth at two-over. (Yonhap News)