Overnight leader Ko closed with a two-under 70 in hot and mostly calm conditions to finish at 10-under 278 for a three-stroke victory over Lee.

Last year's LPGA Rookie of the Year celebrated with the traditional winner's leap into Poppie's Pond.

"It's a really great honour," Ko said on the 18th green.

American Lexi Thompson (67) was solo third at six under while Spain's Carlota Ciganda (68) and In-Kyung Kim (74) shared fourth.

Queensland’s Katherine Kirk was in halfway contention but faded over the weekend with rounds of 74 and 73 to be tied 17th on two under, one shot ahead of countrywoman and World No.3 Minjee Lee, who closed with a 71.

RIGHT: Ko reacts after making birdie on the 18th hole and winning her maiden major championship. PHOTO: Matthew Stockman/Getty Images.

After bogeys on 13 and 15 cut her lead to a stroke, Ko made a six-foot birdie putt on the par-4 16th and closed with a 15-foot birdie putt on the par-5 18th.

The 23-year-old won for the fourth time on the LPGA Tour, completing a desert sweep after taking the Founders Cup in Phoenix. She leads the money list and has five top-three finishes in six events this year.

Ko became the fifth Korean winner of the event after Grace Park (2004), Yoo Sun-young (2012), Inbee Park (2013) and So Yeon Ryu (2017).

Lee parred the final six holes in a two-under 70.

"This is really good momentum for me," she said.

"I'm so happy with this week."