She became the fourth Amateur in U.S. Women's Open history to finish solo second place, and the first since 1998.
The 17-year-old South Korean was poised to become the second amateur to win the biggest title in women's golf, joining 1967 champion Catherine Lacoste of France.
The 23-year-old Park, runaway favorite to win LPGA Rookie of the Year honors, birdied the par-five 15th to forge ahead and, after co-leader amateur Choi Hye-jin double-bogeyed the 16th, added a six-foot birdie at the 17th for some cushion.
It marked the second straight year she has been the low amateur.
And when she curled in an eight-foot birdie putt on the 15th hole to tie Park for the lead at 10-under, it seemed as if it this was going to be a historic day.
The irony wasn't lost on Lee, whose 77 a day earlier cost her any chance of the year's third major, won by Sung Hyun Park in dramatic circumstances at 11 under.
The Perth ace drilled seven birdies at Bedminster, New Jersey, to shoot the day's best round - a six-under-par 66 and vault to four under.
However, Park tied for the lead with a 20-foot gain on the 15th. A double-bogey 5 dropped her three strokes back as Park birdied the 17th hole, the hardest hole on the course. "It's nearly like I'm floating on a cloud in the sky", Park said through an interpreter after signing for 11-under 277.
That left Feng needing an eagle at the last to force a play-off, but her triple bogey sent her tumbling down the leaderboard.
Park won $900,000 U.S. for finishing first.
England's Charley Hull closed with a one-over 73 to finish in a tie for 21st place on level par.
Park, who had led after 36 holes in 2016, started the final round two strokes behind Feng, the leader after each of the first three rounds. That's Cristie Kerr, who was five shots off the lead.
Park, the event's seventh South Korean victor in 10 years, finished on 11-under at Trump National to defeat 17-year-old South Korean amateur Choi Hye-jin by two strokes.
"I was trying to squeeze that distance, and maybe that extra effort somehow ended up in the missed shot", Choi said.
McCarron shot a bogey-free, 6-under 66 to make up a six-shot deficit and beat Langer and Brandt Jobe by a stroke.
From there, she chipped to within three feet and made the putt to save par.
"I look back, I should be happy actually about my result", she said, "because coming into this week I had no expectations at all". "I just couldn't get the line and the speed together".
"I get the runner-up, and it is unbelievably joyous for me", she said.
The walk from the 18th green to the scoring area at Trump National Golf Club doesn't take very long.
South Koreans Sei Young Kim (69), Mirim Lee (72) and Amy Yang (75) tied for eighth at 5 under.
Park was competing in just her second Women's Open.
"I really didn't pay attention to the weather and just concentrated on every shot".
She led all players with 18 birdies, 12 of which came on her last 27 holes.
Kiwi golfer Lydia Ko made a great comeback in her second round at the U.S. women's Open this morning in New Jersey after a poor start on the front nine in Bedminster, New Jersey. And the Ryder Cup player hit a fantastic shot into the final green when the two returned in the play-off to set up a tap-in birdie and secure the third Tour title of his career.