The big leap came on the heels of Lee's playoff victory at the ANA Inspiration in Rancho Mirage, California, on Sunday (local time).
Korda has secured three top-10 finishes in majors previously as she chases a maiden title.
South Korea star produces miracle shot to get into play-off, then calmly scores a birdie for the title.
Stephanie Meadow had a less enjoyable day and her round of 76 was her worst of the tournament as she hit five bogeys to finish on +2 for a share of 51st place.
Lee's career high in the world rankings is 12th from 2015.
© APWF Mirim Lee, of South Korea, watches her tee shot on the 17th hole during the final round to win the on the first hole during the final round of the LPGA's ANA Inspiration golf tournament at Mission Hills Country Club in Rancho Mirage, Calif., Sunday Sept. 13, 2020. Lee is one of many Korean golfers to join the LPGA Tour after paying on the KLPGA Tour.
But Korda, daughter of former Australian Open tennis champion Petr Korda, saw her game become a little ragged around the turn as she mixed three bogeys with two birdies in an up-and-down five-hole stretch, with Henderson matching her two at the 11th to stay tied for the lead.
Back on 18th for the first playoff hole Lee once again relied on her wedge chipping to within five feet and making a nervy putt for birdie with Henderson and Korda both carding pars.
Korda, who had led after every round, had looked poised to claim a first Major victory when she stepped onto the 18th tee with a one-shot lead but a few minutes later found herself in the play-off. She double-bogeyed the hole.
Lee hit a lovely fairway metal that led to her up-and-down for birdie.
Korda had bounced back well from a torrid front nine on Saturday, and she made the best start of the leaders with birdies at three of the first six holes, with Henderson picking up shots at the second and fourth. She followed that up with an approach shot that left her with a long birdie putt, which came up short.
She hit 5-wood just through the green - no help needed from the wall on that one - chipped to 5 feet and made the birdie putt.
The 29-year-old, who claimed her fourth LPGA victory and her first since the 2017 Kia Classic, added later: "To be honest, I feel like I must be a little insane for winning and for having won this, and I think I'll be able to feel it once I meet my family and reunite with them".
Doc Redman closed with a 62 - matching the lowest round of the tournament - to tie with Brian Stuard (70), Chez Reavie (66) and Kevin Streelman (67) at 18 under.
The chalet in normal years has served as a buffer for shots struck too hard, but it served no goal except for some signage that didn't really stand out.