Park In-Bee downed Brittany Lincicome with a par at the first playoff hole on Sunday to win a second-straight LPGA Championship title.
The South Korean star claimed the fifth major title of her career.
Three of those came in her stunning six-win 2013 campaign, but she hadn't notched a win in 2014 until the Manulife Financial Classic in Canada in June.
"I'm very happy to defend my title and actually have a second win of the year," said Park, who couldn't match Lincicome's length off the tee but was able to compensate with other aspects of her game at Monroe Golf Club.
"I think I had to hit a lot of shots closer from longer distance, obviously," Park said. "I had to make a lot of putts."
Park, who started the day tied for second with Suzann Pettersen one stroke behind Lincicome, fired a two-under par 70 for a 277 total.
She birdied 17 and drained a long par putt at the last to keep the pressure on Lincicome, who could have won in regulation with a par at the final hole but bogeyed the 72nd to cap a 71 and fall into the playoff.
They returned to the par-four 18th for the first hole of the sudden death decider and both failed to find the green with their second shots. Lincicome's chip rolled six feet past the hole while Park chipped up to about three feet.
After Lincicome's par effort burned the edge but failed to drop, Park rolled in her tournament-winner.
New Zealand's 17-year-old Lydia Ko finished third after a 70 for 280.
It was a further two strokes back to Spain's Azahara Munoz, who signed for a 70 and Sweden's Anna Nordqvist, who notched a 71 for 282.
Former world number-one Park, who is projected rise from her current third to second in the world rankings, is the first player to defend the LPGA Championship title since Swedish great Annika Sorenstam won her third straight in 2005.
Lincicome, who saw her three-stroke 36-hole lead dwindle to one after Saturday's third round, opened with two pars.
Park was even through three and Pettersen fell off the pace with a double-bogey at the first.
The Norwegian never really recovered and signed for a 76 that left her sharing sixth on five-under.
Park's first birdie of the day on number four briefly moved her into a tie for first, but Lincicome responded with a birdie at the third.
Almost as soon as Park had bogeyed the seventh, Lincicome dropped a shot at the sixth.
Lincicome drained a 10-foot birdie putt at the eighth to get to minus-11 again and move two shots clear of Park.
She stretched her lead to three with a birdie at the 11th, but Park gained another shot on 12 to remain two back.
A poor chip led to a bogey at the 12th for Lincicome but a birdie at 14 stretched her lead back to two.
At 17 Park drained a long birdie putt to move within one shot of Lincicome, and she rolled in another long one for par at 18.
Needing a par to win on the 18th, Lincicome -- who admitted she had trouble conquering her nerves -- found the fringe with her approach. She left her first putt 10 feet short and her par putt slid by on the left.
"I think it's very lucky that I actually got an opportunity today. I thought I probably won't get an opportunity with Brittany coming up the last and if she made a par I would not have gone into playoff," Park said.
"And I holed really good putts on number 17 and 18 to put me in the playoffs. So yeah, just very happy with the way I played today."