She goes by the nickname, "Dak Gong", coined by Korean fans that translates into "just shut your mouth and attack", she explained through an interpreter after starting the final round three back and winning her first major by two shots.
"It's nearly like I'm floating on a cloud in the sky", Park said. "Coming into this week I had no expectation at all".
Park, who finished tied for third at last year's U.S. Women's Open, took home $900,000 of a $5 million purse. With a powerfully fluid swing, she is fifth on tour in driving distance, slamming it out there more than 274 yards a pop.
Choi held the lead alone at one point and also shared the lead.
Then, trouble struck. Choi tried to be too flawless with her tee shot on the 139-yard hole and deposited it right into the lake.
Top-ranked So Yeon Ryu (70) and fellow South Korean Mi Jung Hur (68) tied for third at 7 under.
Her previous best finish this year was second place at May's LPGA Volvik Championship.
Feng looked to be in control when she birdied the 10th from close range and Choi missed an eight footer for par.
England's Charley Hull mixed five birdies with three bogeys in a round of 70 that propelled her into a share of 14th on two under. Park made birdie at the 12th to make it a three-way tie for the lead.More news: Emily Blunt Debuts New 'Mary Poppins Returns' Content at D23!
After taking a drop, Choi settled for a double bogey. She has only one bogey through 54 holes.
The 27-year-old Rio Olympic bronze medalist missed her only fairway of the day at the par-5 18th, sending her tee shot into the deep left rough. She appeared remarkably poised until her error on the 16th, which came right in front of the president's tent, where Donald Trump was looking on.
Park prides herself on her ability to maintain her focus in the heat of competition.
"I think one of the most hard things is to to stay focused and keep that concentration level up", she said, "because I know that once you lose it, your playing is going to go just sideways". I tried to pull my shot and it didn't happen. "But I had to refocus back for the two remaining holes".
Feng lost her hold in the lead for the first time when she bogeyed the sixth hole, but she was 1 under for the rest of her round until she misfired at the finish. But she was satisfied with her week's work. "And, you know, I'm not surprised that she won this week because I was just talking to my friends, I said, 'As good as she is, she's going to win anytime.' So, yeah, I'm happy about her, for her".
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.
Bad weather then forced a lengthy delay, with some players still to finish their opening round when darkness forced an end to proceedings shortly after 8.30pm local time. Seven other players have won one each.
Marina Alex of nearby Wayne, N.J., was the best of the Americans at 4 under after 70.