Park, just 16 years old, had six birdies and one bogey at the Swope Memorial Golf Course. She is one shot ahead of Tiffany Chudy and Mari Chun. Hannah Jun and Jenny Suh are each two strokes back, while Jessica Soltes, Marina Choi and Jackie Beers are each at minus-2.
Park birdied the par-4, 317-yard second hole before taking a bogey four at the following hole. She also birdied holes seven, nine, 13, 16 and 18.
Last year, Park lost to Michelle Wie in the semifinals of match play at the tournament. This week, Wie is playing in the Men's Amateur Public Links Championship.
The final round of qualification stroke play is Tuesday. The field will then be reduced from 144 to the top 64 players, who will advance to match play.
After Tuesday, the tournament heads into match play. The first 18 holes are Wednesday, followed by the second and third rounds on Thursday. The quarterfinals and semifinals are Friday and the 36-hole final is Saturday.