Ryu So-yeon claimed the US Women's Open at Colorado Springs by three shots in a three-hole play-off, her first victory in America and her maiden major title.
The year's third major had been heavily disrupted by rain, thunder and lightning over the previous four days.
Ryu, 21, was one shot behind with three holes to play when play was suspended on Sunday evening due to fading light.
She birdied the final hole to force a play-off with Seo Hee-kyung and then finished two under in the play-off.
Ryu is the third South Korean winner in the last four US Women's Open Championships.
Only Pak Se-ri, at 20, and Park In-bee, at 19, have won the coveted title at a younger age.
"I won KLPGA (Korean LPGA) tournaments six times but no majors and now I have won the US Women's Open. I can't believe it," she said.
Having holed from five feet to birdie the final hole of regulation play and join Seo at three under, Ryu and her compatriot competed in a play-off over the 16th, 17th and 18th holes.
Ryu recorded par-birdie-birdie, while Seo's title bid effectively ended at the par-five 17th, where she found the lip of a fairway bunker off the tee and could advance her second shot only 100 yards.
From deep rough in front of the green, she then struck a wedge to 18 feet and missed the par putt to trail Ryu by two strokes, her fellow Korean having holed from 12 feet for a birdie.
World number two Cristie Kerr, who won the event in 2007 and claimed the LPGA Championship last year, finished alone in third at one under after closing with a 71.
"I was in contention but I made one bad swing on the 10th hole, in the second round," Kerr said. "I made a triple and a couple of three-putts. To win the Open, you can't do that."
Karen Stupples was the leading British player after carding a final round of 68 at The Broadmoor's East Course to finish in a share of 15th place at six over.