Kim had a double bogey on No. 3 to fall back. She played 2 under the rest of the way, but that one bad hole allowed Park to put some distance between them.
"She is playing great. But you never know, I might have a great day tomorrow," Kim said. "So golf is a different thing than other sports. That's why you play four rounds."
If Park shoots even-par or better Sunday, it will be just the fourth time the U.S. Women's Open was won with a score in double digits below par.
No wonder Brittany Lincicome joked to reporters, "I think Inbee's playing a different golf course, which you guys are unaware of yet."
Certainly feels that way.
With Park again on a different plane from the rest of the field, the biggest excitement Saturday might have come when Jessica Korda fired her caddie after nine holes and replaced him with her boyfriend.
The switch seemed to work: After shooting 5 over on the front nine, Korda was 1 under the rest of the way. She finished with a 76 and was tied for sixth at 1 over, 11 strokes behind Park.
The 2008 U.S. Women's Open champion, Park has already won five times this year, including her last two tournaments.
"I'm just going to think that I.K. and I am tied starting in tomorrow's play because anything can happen out here," she said. "I mean, four shots, it could be nothing around this golf course. So I just have to keep pushing myself to make pars. I think par is going to be good enough tomorrow, but I'm just going to try to do my best. A lot of thinking going on, a lot of pressure.
"But I've done that before, so I think the experience is going to help me going through it tomorrow."