Ko led by five shots with six holes to play, only to collapse down the stretch when in sight of her first victory in 27 months.
From sitting at 18-under par and ready to cruise to victory, Ko bogied the 14th and 15th holes, as world No 2 and last week's winner Danielle Kang came storming back with birdies on 13 and 14 to close the gap.
It looked as if Ko had stabilised, and went into the final hole, a par-five, still with a one-shot lead, but her second shot went onto the cart path, her third across the green and into the rough and her fourth was the worst of them all, with a chip shot rolling back down the slope and into the bunker.
Once she was finally on the green, Kang had parred the hole, and Ko was left needing to hole a bogey putt merely to force a playoff.
She couldn't, and the double bogey saw her sign for a 73 and a share of second, and the best opportunity she's had in years to win a tournament disappear.
