Park didn't make a bogey over the final 10 holes, pulling away with three clutch putts early on the back nine and building a four-shot lead going to the final hole. She finished with a tap-in birdie, and a few of her fellow South Koreans doused her with beer.
The victory came 10 years after Park took up the game, inspired by watching Se Ri Pak win the Women's Open at Blackwolf Run to become the youngest champion at age 20.
"It's really an honor and very special for me that I won the event 10 years after I start playing," Park said. "Everything happened so fast. It's scary. I really tried to stay calm, but it was so exciting, I couldn't do it. This is my day."
Park finished at 9-under 283 and earned $585,000 from the richest purse in women's golf. Her four-shot victory over Helen Alfredsson of Sweden was the largest in the Women's Open since Karrie Webb won by eight shots at Pine Needles in 2001.
No one imagined the only drama on the back nine would come from Annika Sorenstam, who was never in contention competing in her final Women's Open before retirement at the end of the season.
Her final shot was a 6-iron from 199 yards that tumbled into the cup for eagle.
"Leaving with another great memory, that's for sure," Sorenstam said after closing with a 78 to finish 12 shots behind in a tie for 24th. "Maybe not the one I had in mind, but I'll take it."
Such highlights were rare for everyone else.
Stacy Lewis, trying to become the first player to win a major in her professional debut, took double bogey from 80 yards away on the par-5 second hole and struggled all afternoon with her lag putting. She staggered home to a 79 and tied for third at 4-under 288 with Angela Park (73) and In-Kyung Kim (75).
An even greater collapse came from Paula Creamer, 21, who said her experience from six LPGA Tour victories would be a big advantage. She then shot 41 on the front nine, including two double bogeys, and wound up with a 78 to tie for sixth.
Creamer's final round scoring average in the U.S. Women's Open is 75.2
Park was the only player to break par all four days at Interlachen, a course that showed its strength in the final round with 20 mph wind that made it tough to keep on the right side of the hole.
The lowest score Sunday belonged to 15-year-old Jessica Korda, the daughter of '98 Australian Open tennis champion Peter Korda, who caddied for her. She shot a 69 and tied for 19th.
Park became the third player in the last six years to make the U.S. Women's Open her first LPGA Tour victory, and it was reminiscent of Birdie Kim's victory three years ago Cherry Hills, minus the dramatic bunker shot for birdie on the 72nd hole.
There were so many possibility for great story lines going into the final round – Lewis and her remarkable recovery from back surgery that almost ended her career before she got to college; Creamer, looking poised to finally get a major to go with her marketing campaign; Alfredsson, who blew a six-shot lead at the Women's Open in 1994, now with a chance for redemption at 43.
Instead, it was Park who stole the show by simply playing the best golf.