Seon Woo Bae, a victor in South Korea previous year, was alone in fifth place at 5 under after a 69.
Sung Hyun Park, who last year let the U.S. Women's Open slip away from her, outdueled Shanshan Feng and 17-year-old amateur Hye-Jin Choi in a goose bump filled final round at Trump National.
With two holes remaining, Park shared the lead with Choi, a 17-year-old from South Korean who was attempting to become the youngest-ever victor of the premier title in women's golf, and just the second amateur to win the championship, joining 1967 victor Catherine Lacoste.
But not only is Park skilled, she also has manners, as she was captured bowing to US President and course owner Donald Trump in the final round... "But the big issue was 17, hitting a disgusting shot there and then missing for bogey".
"I think I did really well for the first three days, and then I'm going to stick to my game plan tomorrow".
USA president Donald Trump attended the biggest event in women's golf for the third straight day. There were threats of protests, especially after Trump made a decision to attend the tournament after his trip to Paris on Thursday and Friday. Five protesters (four women, one man) staged a demonstration beneath his box that overlooked the 15th green and 16th tee. She flew the green with her third shot at the par 5, leaving a long uphill recovery shot with water in play.
She has played steady throughout the week, shooting 69-69-70 in the first three rounds.
Park continued to thrive on the LPGA of Korea Tour the following year, winning no less than six events.
"It's nearly like I'm floating on a cloud in the sky", Park said. She is the eighth South Korean victor of the U.S. Women's Open.
Choi is a member of the Korean national team and is No. 2 in the World Amateur Golf Ranking, and no stranger to success at a young age, tying for seventh at the LPGA's ISPS Handa Women's Australian Open earlier this year. It would have placed her in 22nd place on the 2016 money list had she been a full member.
"Well, I mean it will be nice if I could get the money but I think my primary goal was to come here and compete so, to me, getting this second place as runner-up actually means more to me and it's a greater honour for me", Choi said through an interpreter.
World number one Ryu So-yeon of South Korea (70) and compatriot Hur Mi-jung (68) shared third on seven-under.
That put the Olympic bronze medal victor two clear of Korean trio Hye Jin Choi (69), Jeongeun Lee (69) and Amy Yang (71).
On a dramatic final day and closing few holes, Park and Choi were tied at 10 under and one ahead of long-time leader, Feng, as Choi stood on the 16th tee with Park in the group ahead playing the 17th. She ended with a double bogey and basically lost her chance of winning.
Frenchwoman Catherine Lacoste (1967) remains the only amateur to have won arguably women's golf's most prized crown.
South Korean golfers have won the US Women's Open seven times in the past 10 years, and there were eight in the top 10 this year. Her total of 279 beat the old amateur record, set by Grace Park in 1999, by four strokes. "But I keep in mind to stick with how I usually play because it was part of my practice and I stuck with it and I did it".