In this Associated Press photo, Kim In-kyung of South Korea watches her shot at the fourth hole during the final round of the Evian Championship on the LPGA Tour in Evian-les-Bains, France, on September 17, 2017.
But with the final hole bogey, she dropped to eight under par, one shot behind Brittany Altomare and Anna Nordqvist.
In torrential rain, Nordqvist won at the first extra hole with a bogey five.
At that point, Ko was at six-under, four shots back of leader Moriya Jutanugarn, but she slowly gained back that ground.
The fifth women's major of the season is a 54-hole event after Thursday's scheduled first round was rained out.
Kim Sei-young was the top finisher from the South Korean contingent at the weather-shortened Evian Championship at par-71 Evian Resort Golf Club in Evian-les-Bains, France, where she tied for sixth at seven-under 206.
Last month, Jutanugarn was in second place and in the final Sunday pairing at the Ricoh Women's British Open at Kingsbarns.
The 33-year-old, who has yet to win on the U.S. LPGA tour, had seven birdies and two bogeys for a two-round total of 8-under-par 134, one back of Thailand's Moriya Jutanugarn.
No season has ever had more than two first-time winners at major championships. Nordqvist eagled the par-5 15th to begin her path to victory.
In her final round as a professional before retiring, two-time Evian victor Ai Miyazato shot 73 to finish 1 over. The condition sidelined her throughout the summer, resulting in her coming up one event short of the required number events needed to qualify for the European Solheim Cup team. While the 23-year-old Thai was making bogey-6 at the 13th, Nordqvist made an eagle-3 and birdie to be alone on 10 under. "I thought it was just for second", said Altomare. I mean, I'll probably think a bit more about it tonight and next week, and be a little bit maybe bittersweet about it. She drained a huge putt to save par at the 18 to remain at nine-under par and cap off a Sunday, 66 to match her low round of the year.
"I just felt like I wanted to go out there today and focus on what I could do".
"I'm looking forward to finishing off the year and maybe get another W. The girls are so good out here; it's just fun to be able to compete again and know I've got the right stuff".
Su Oh completed a good tournament with a final round of 70 to finish in a share of 14th Minjee Lee was 32nd and Sarah Jane Smith 48th.