She closed with a 2-under 69 in the final round to match her two rivals at 14-under 270, and off they went, up and down from tee to green four times.
"Not a very easy hole," Ko said. "With the wind blowing left to right and the pin tucked on the left, it was probably the toughest it'll play. I think we were all getting a little bit physically and mentally tired as we were continuing to play the same hole."
The New Zealander is 4-1 in playoffs, with the loss coming to Brooke Henderson this year in the KPMG Women's PGA.
It was a topsy-turvy playoff. Ko missed a 5-foot birdie putt on the third extra hole, sending the trio back to the 18th tee for the final time. Jutanugarn had a good chance on the second playoff hole, but missed an 8-footer.
Ko posted rounds of 68, 66 and 67 to start the final day three shots behind Hyo Joo Kim. Three birdies in the first six holes, as Kim had three bogeys over the same ground, had Ko on target. But she bogeyed 14 and 16 before finishing with two pars. Lee shot a fine 65, bogeying the last to lose the outright lead. Jutanugarn had a 68, and got to 14-under with an eagle on the 17th. Kim finished one shot behind the leading trio.
Ko's next assignment is expected to be the British Open at Milton Keynes, starting on July 28.
• New Zealand will have three golfers at the Rio Olympics, with Danny Lee, Ryan Fox and Ko confirmed for the event yesterday.
While world Nos 1 and 40, Ko and Lee, were shoe-ins, Fox had to scrap to hold off Michael Hendry's challenge, then had a nervous wait to get New Zealand Olympic Committee approval.
The naming is extra special for Fox. His grandfather, Merv Wallace played cricket for New Zealand in the 1930s and 1940s, and dad Grant Fox was an All Black World Cup winner in 1987.
"Obviously it's a pinnacle sporting event and I can say I'm the third generation of my family to represent New Zealand in three different sports, so it's a pretty cool thing to be able to do," said Fox.
New Zealand's team for Rio now sits at 198, with marathoner Paul Martelletti having an appeal lodged with the Sports Tribunal.
On a roll
• Lydia Ko has now pocketed US$7.145 million in career earnings; US$2.255m this year.
• She has won four titles this year on the LPGA Tour, had three seconds, two shares of third, and only four finishes in double figures out of 15 starts.
• On the LPGA Tour stats, Ko sits No 1 for rounds in the 60s, rounds under par, putting average and scoring average this year.