Kim recovered from four shots behind in a dramatic final round to clinch victory over world No.2 Jeeno Thitikul on the second playoff hole at the Evian Championship in France.
Thitikul appeared on track to herself capture her maiden major after a trio of Australia's aces faltered down the stretch at the Evian Resort Club on Sunday.
Gabriela Ruffels shared the lead while fellow 24-year-old Kim and triple major-winning great Minjee 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 the 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.
Kim's epic victory secured Australia a second straight major after Minjee Lee won the Women's PGA Championship only three weeks ago.
After starting the final round tied with Kim in equal second, Lee ultimately finished joint runner-up.
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