Park, 16, defeated Felicia Johnston, 7 and 6. Park, who is from Torrance, Calif., and is seeded second at the tournament, will next take on Juli Wightman of Chicopee, Mass. Wightman defeated Lacey Jones, 6 and 5.
The 17-year-old Chun, the top overall seed from Pearl City, Hawaii, cruised past Patty Chawalitmetha, 4 and 3. Her next opponent will be 32nd seed Renee Skidmore of Everett, Wash., a 4-and-2 winner over Sara Brown.
Defending champion Ya-Ni Tseng of Chinese Taipei, the 58th seed, upset No. 7 Sung Lee, 3 and 1. Tseng will next take on Mariko Shimozaki of Kihei, Hawaii Thursday morning.
'I slept with my putter last night because it didn't work on the second day (of stroke play),' Tseng said through an interpreter. 'I will sleep with my putter again and get a lot accomplished.'
Tseng defeated Michelle Wie in last year's final. Wie is playing in the Men's Amateur Public Links this week in Lebanon, Ohio.
Third seed Marina Choi of Los Angeles won her match in a one-hole playoff with Sarah Tiller. Fourth seed Jackie Beers of Bonaire, Ga., was upset, 4 and 3, by Christi Athas of Eldora, Iowa.
The field now stands at 32 players. There will be only eight players left come Thursday night. The event will conclude with the 36-hole championship final on Saturday.
The U.S. Women's Amateur Public Links is one of 10 national championships for amateurs conducted annually by the USGA. The association also conducts the U.S. Open, U.S. Women's Open and the U.S. Senior Open.