Lee relinquished a two-shot advantage with three holes to play, then three-putted the first extra hole as former World No.1 Jin Young Ko rallied for a thrilling third victory.

Starting the final round four strokes off the pace, Ko closed with a Sunday-best 67 to join Lee (71) at 13-under-par and force the play-off.

In a showdown of multiple major champions, Ko held firm as Lee faltered to leave the South Korean to add the title and US$450,000 (A$677,000) winner's cheque to her 2019 and 2021 Founders Cup trophy collection.

Playing the par-4 18th again, Lee had a 20-foot putt from the fringe to defend the trophy she won last year, only to put it six feet past and then miss the return for a surprise bogey.

The World No.6's deflating finish came barely an hour after Jason Day snapped a five-year, two-month PGA Tour title drought at the AT&T Byron Nelson Championship in Dallas.

Lee never produced her best golf on Sunday but did look every bit the winner standing on the 16th tee.

RIGHT: Jin Young Ko claimed a third Founders Cup title after the play-off win over Minjee Lee. PHOTO: Mike Stobe/Getty Images.

The West Australian had let a three-shot overnight lead slip after finding the water and posting a dreaded double-bogey five on the par-5 6th.

But she tenaciously clawed her way back with a birdie at the next hole before adding three more on the back nine to charge two shots in front.

Alas, a three-putt on the 17th opened the door for Kim, who marched through with a long bomb for a birdie at the last before the World No.3's par at the first extra hole proved good enough for victory.

"I heard the roar when Jin Young birdied 18, so I knew I was probably going to be tied if I didn't birdie the last hole," Lee said.

"I chipped it really well and it just missed, but I still think I played really solid today and throughout the whole week."

Grace Kim continued her outstanding rookie year form to share 10th at four-under, while Sarah Kemp was a shot further back in T13 with Karis Davidson and Steph Kyriacou rounding out the Aussie contingent to make the weekend in a share of 31st.