Kim, with an afternoon tee time playing the major for the first time, wondered, ''Wow, how did she shoot that score?''
Then Kim went out on Thursday and shot one stroke better, finishing with a bogey-free 6-under 66 to take the first-round lead at Sebonack Golf Club.
Park is trying to make history by winning the first three majors of the year. For a day at least, she was upstaged by a much less heralded fellow South Korean.
''I'm enjoying myself,'' Kim said through a translator. ''I'm just happy to be here and to be playing in this big event. I'm not really thinking about winning or results but enjoying the moment.''
Currently a member of the KLPGA Tour, Kim is a seven-time winner in South Korea. She kept giving herself short birdie putts on Thursday and making them.
Kim birdied her second-to-last hole with daylight waning to claim the lead after Park held it for most of the day with her 67 in the morning session.
No player has won the first three majors in a season with at least four majors. Park, the 2008 U.S. Women's Open champion, has already won five times this year, including her last two tournaments.
Concerned about bad weather, tournament officials moved up the tees, and with the rain holding off, Park was able to play aggressively.
''I never had practiced from those tees, so I was a little bit shocked when I went to the tees,'' Park said.
Not that she was complaining.
She repeatedly set up short putts, and the way she has excelled in her short game lately, Park was headed to a low score.
''So instead of hitting like 5-irons, we were hitting 9-irons, and that was making the course much easier,'' she said. ''I was actually able to go for some pins and give myself a lot of opportunities today. I made a lot of putts and didn't leave much out there.''
Starting on No. 10, Park birdied her first hole, then started racking up pars. She made the turn at 2 under before birdies on three of her next four holes.
At 5 under, Park briefly struggled with her tee shots, needing to save par on Nos. 5 and 7. On No. 6, her 15th hole of the day, she had to lay up out of the tall grass and settle for her lone bogey.
Park got back to 5 under on the par-5 eighth with a chip shot to about 5 feet that set up a birdie putt.
Hedwall and I.K. Kim were each at 5 under with a hole left but closed with bogeys. Nordqvist birdied her last two holes to pull into the tie for third.
The two Swedes grew up playing together.
''Certainly seeing her shooting 4 under in the morning session gave me a little bit of inspiration for the afternoon,'' Nordqvist said.
Salas, a 23-year-old former Southern California star, played with Park in the last group of the final round of this year's Kraft Nabisco Championship. Three strokes back starting the day, she opened with a double bogey and tumbled to 25th after shooting a 79.
She bounced back to reach a playoff at the LPGA Lotte Championship in April, losing to Suzann Pettersen for her best LPGA finish.
''I'm just getting a lot more used to being in contention and really studying the leaderboard and really managing my patience,'' Salas said. ''I think that's been key for me this week. Yes, I still get nervous on the first tee and my hands keep shaking, but I just know that if I just trust myself and trust my instincts, I can perform out here.''
Chile's Paz Echeverria, a 28-year-old LPGA rookie also making her U.S. Women's Open debut, and Canada's Maude-Aimee Leblanc shot 69.
Among eight players at 70 was Natalie Gulbis, who withdrew from a tournament and missed two others earlier this year because of malaria. Infected by a mosquito during the LPGA Thailand in late February, she returned for the Kraft Nabisco in early April. Gulbis hasn't finished better than 13th since, missing the cut at the LPGA Championship.
Lydia Ko, the 16-year-old New Zealand amateur who won the Canadian Open last August to become the youngest LPGA winner, had a 72.
Michelle Wie opened her round with a quadruple-bogey 8 on No. 10. She was at 11 over through 14 holes before birdies on three of the last four to finish with an 80.
With Park's two major titles to start the year, South Koreans have won four straight majors. But Ha-Neul Kim was an unlikely representative to lead after the first round of this tournament.
''I was very nervous coming in, and I thought in the practice round that the course was very difficult,'' she said. ''Before playing today, I thought that even par would be a very good score for me.''