Park shot her second straight 5-under 67 on Sunday and won a final-round battle with front-running Shanshan Feng and teenage amateur Hye-Jin Choi at Trump National Golf Club for her first LPGA Tour victory.
Park birdied the 15th to move into a tie for the lead and the 17th to open a two-shot edge after Choi made a double bogey on the previous hole. Park finished at 11-under 277 for a two-stroke win over Choi.
President Donald Trump attended the biggest event in women's golf for the third straight day. There was a peaceful protest after he arrived at his box near the 15th green shortly after 3 p.m.
It ended up being a quiet week of politics. The golf was excellent.
Park needed a fine chip from over the green on the par-5 18th hole to save par and win the $900,000 top prize from the $5 million event.
Walking to the scoring tent to sign her card, she got a thumps-up from Trump from his box.
Choi closed with a 71 to finish as the low amateur for the second straight year. She was 38th in 2016.
Top-ranked So Yeon Ryu (70) and fellow South Korean Mi Jung Hur (68) tied for third at 7 under. Feng, from China, had a 75 to drop into a tie for fifth at 6 under with Spain's Carlota Ciganda (70) and South Korea's Jeongeun6 Lee (71).
South Koreans Sei Young Kim (69), Mirim Lee (72) and Amy Yang (75) tied for eighth at 5 under. Marina Alex of nearby Wayne, New Jersey, was the best of the American at 4 under after a 70. It was the worst finish in the Open for the top American since Paula Creamer was seventh in 2012.
Choi was the story for most of the final round. The 17-year-old had a two-shot lead with nine holes to play and needed a birdie at 15 to regain a piece with Park.
The 139-yard, par-3 16th over water ended her hopes. Her 7-iron landed in the water to the right of the hole. She ended with a double bogey and basically lost her chance of becoming the second amateur to win the Open.
"At the time I felt that all this work, hard work I put together was going to disappear so I was bit disappointed but I had to refocus," said Choi, who birdied the final hole but could not collect the $540,000 second prize because of her amateur status.
Choi's 279 was the best by an amateur in the Open, four shots better than the old mark by Grace Park in 1999. Catherine Lacoste remains the only amateur to win the Open, doing it in 1967.
Feng, who was the leader after the first three rounds and carried a one-shot edge into the final 18 holes, triple bogeyed the final hole.
"I think overall, before the last hole I did pretty well," said Feng, who had only two birdies in the last two rounds. "I mean I did a good job hanging in right there because my putting was not really that great."
The win was redemption for Park, who is the leading rookie on the LPGA Tour this year. She had the 36-hole lead in the Open last year and shot final rounds of 74-74 to finish two shots out of a playoff with eventual champion Brittany Lang and Anna Nordqvist.
Park saved her best for the last two rounds this year and won. It was not her first professional win, she won seven times on the KLPGA Tour in 2016 and three times the year before.
"She's young and long so she hits the ball very long and very straight, very accurate and has very good short game, also," Feng said about Park. "I don't see any weak part in her game."
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