Kiwi Lydia Ko has lost ground on the leaders at the Women's LPGA Championship in IL, slipping to a share of 10th place.
Park defeated countrywoman Ryu So-yeon on the second playoff hole to claim the KPMG Women's PGA Championship at Kemper Lakes Golf Course in Kildeer, Illinois, on Sunday (local time).
Ryu also used a neat approach on 18 to set up a short birdie putt on the par-4 hole.
After making the championship-clinching putt, Park raised both arms in celebration and shed tears - a rarity for a golfer who has been known to show very little emotion, positive or negative - in tournaments.
Nasa Hataoka, who had come out of nowhere with a final-round 64 that included two eagles, had been eliminated on the first playoff hole.
And then I was able to make a birdie putt after all. Park finished regulation at 3-under 69 for the round and 10-under 278 for the tournament after starting Sunday four strokes behind Ryu. She took a two-stroke lead on the 16th, but hit into the water on the par-3 17th en route to a double bogey. She made a brilliant par save on 16 after she dug out from the water's edge.
Nine strokes behind Ryu entering the day, the 19-year-old Hataoka almost pulled off one of the biggest comebacks in LPGA Tour history.
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Hataoka, 19, won her first LPGA title last week in Arkansas and with more than US$546,000 in the past eight days has eclipsed her prior career earnings. She shot a 5-under 67 on another scorching afternoon to get to 11-under 205 and move closer to her third major victory.
Park almost took a one-shot lead at the 17th, but her long birdie attempt lipped out.
As is often the case with golf, the South Korean had her fair share of luck along the way too.
Things would remain that way to set up the second playoff in an LPGA Tour major this year. The heavily favored Team Republic of Korea will feature Inbee Park, Sung Hyun Park, So Yeon Ryu and In-Kyung Kim, who finished in a tie for 8th on Sunday to jump past Hye Jin Choi for the fourth spot on the team.
Ryu was the overnight leader at 11-under but committed two double bogeys for a 73 in the final round, while blowing a two-shot lead with two holes to play to fall into the playoff. The changes were effective for Park, as she had 27 putts in the final round and not a single bogey. But she quickly responded by hitting a high-arcing shot that landed within two feet of the cup to stay in contention.
The two-time major champion from South Korea posted one of the few sub-par rounds in the morning at the Kemper Lakes course.