Kim recovered from four shots behind in a most dramatic final round to clinch victory over world No.2 Jeeno Thitikul on the second playoff hole at the Evian Championship in France.
With three crazy eagles in a final-round 67, Kim prevailed with a 14-under-par 270 winning total to join Karrie Webb, Minjee Lee, Hannah Green and Jan Stephenson as only Australia's fifth female major winner.
Thitikul appeared on track to herself capture her maiden major after Kim, Lee and Gabriela Ruffels faltered down the stretch at the Evian Resort Club on Sunday.
Ruffels shared the lead while fellow 24-year-old Kim and triple major-winning great Lee were just one shot behind entering the final round in the beautiful French Alps, near Lake Geneva.
After a rollercoaster day of twists and turns, Kim found herself in a playoff with Thitikul after delivering a contender for shot of the year for a spectacular eagle on the closing par-5 18th hole.
Thitikul still had the chance to win but missed a short sliding downhill putt before Kim tapped in for eagle to force the playoff.
The Thai then looked certain to win on the first extra hole when Kim hit her second shot into the hazard.
But the Sydneysider miraculously chipped in for birdie to extend the playoff, before prevailing on the second extra hole when Thitikul erred again and could not match Kim's eagle.
"It just worked out great," Kim said.
"I doubled 12 and I thought I was out of it.
"But I just said to myself and to my caddy, 'I've got nothing else to lose."
Kim's epic victory secured Australia a second straight major after Lee won the Women's PGA Championship only three weeks ago.
After closing with a 67 to post a four-round 14-under-270 total, Kim ultimately only edged out Lee - who closed with a 68 - by one shot.
Ruffels' third-round co-leader and fellow former tennis ace, England's Cara Gainer, was quick to fade out of the picture with four bogeys in the first five holes.
Completing a stellar championship for Australia's exciting batch of stars, 2024 runner-up Steph Kyriacou stormed home with a 64 to tie for 14th.