Back-to-back rounds of 67 on Saturday and Sunday allowed the 23-year-old to improve from seven shots off the 36-hole pace set by Shanshan Feng to win by two over 17-year-old amateur Hye-Jin Choi.
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.
Choi, looking to become the youngest ever to win the US Women’s Open, faced the 139 yards ahead of her and, given the manner in which she had been playing, it appeared as if, despite the dangers of a front-right flag protected by water, there was little to be concerned about.
This, though, was the greatest title in women’s golf at stake and Choi, who had been the leading amateur at last year’s US Open and had earlier in the year won the Australian Amateur Championship, hit a shot she will no doubt want over and over again, finding the water to the right of the green and taking a double bogey to fall two behind.
Ahead, Park was continuing her remarkable round under the most intense pressure and scrutiny, none other than course owner and US President Donald Trump watching on from his high-security marquee.
The two-time runner-up on the LPGA Tour hit an 8-iron close at the 17th and converted, and as she headed to the 18th, was two ahead of Feng and three clear of Choi.
Park - who found water on the 72nd hole at her maiden US Women's Open appearance last year before finishing third - ensured there would be no such mistakes this time.
Laying up at the par-5 18th was the smart thing to do given the margin she held, but she was long with her approach and the possibility of a bogey was still very much on the cards. She would, though, hit the most exquisite of pitches to save par and essentially put the result beyond doubt.
"When I was approaching to make the fourth shot, 18th hole, my mind went completely blank," said Park. "But I remember to stick with how I usually play because it was part of my practice and I stuck with it and I did it.
"Last year, I think toward the end I was getting more anxious and I just wanted to probably reduce the number of stroke, that I was probably pressuring myself. So I think because of that probably made more mistake than I can.
"But this year, I owe to that great experience that I had, I think I learned more and was able to have a better play this time.
"I actually cannot believe that even I am making this acceptance speech, that this is actually happening, but the fact that I guess my name is going to be engraved on it is unbelievable joy and happiness. I am so thankful and happy.
"I recognize lot of my fans flew in from Korea to cheer me at this tournament and also the great Americans who live around here, they were so gracious and hospitable, provide me Korean food day after day so I could nourish myself and gain strength."
Choi found the resolve to birdie the last and would eventually finish alone in second position after her playing partner Feng, almost inexplicably, triple bogeyed the last to drop to a share of 5th position.
It was a gut-wrenching finish for Feng both emotionally and financially, the dropped shots at the last costing her nearly US$370,000.
The Chinese star was trying to put a positive spin on it however.
“Well, I mean I think overall, before the last hole, I did pretty well,” said Feng. “I mean, I did a good job hanging in right there because my putting was not really that great.
“Then, I mean finishing up with a triple bogey on the last, of course, it's not very -- not very necessary but I don't know how I hit it that far on the 3rd shot and then I just lost myself after that and overall, I think I had a great week this week. My second best finish at the U.S. Open. Still a very good experience.
“My last three U.S. Opens, I think I missed two cuts and last year I just made the cut so actually this year is such an improvement. So, I think it's been great.
Mi Jung Hur and So Yeon Ryu tied for 3rd two shots behind the runner-up and four from Park.
The Australians were led by Minjee Lee, whose final round of 66 saw her finish in a share of 11th.
More on the Australians' performances can be read here.
SUNG HYUN PARK'S MAJOR BREAKTHROUGH
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