Park won three of her final four holes to rally for a 2-up win over Sarah Huarte. This was the first all-American semifinal since 1994.
McCurdy, who coasted to a 3 and 2 win over Sun-Young Yoo to reach the semifinals, won the third hole when Creamer missed a short par putt. Creamer, who reached the semifinals in her last four USGA events, stumbled to another bogey at the fifth to slide 2-down.
Creamer bogeyed the seventh, but came right back to birdie the eighth to get back to 2-down. However, McCurdy turned it on from there.
The 20-year-old University of Arkansas student dropped her second 3 feet from the cup at nine. McCurdy sank that birdie try to go 3-up. She two-putted for par at the 11th to extend her lead to 4-up.
McCurdy, playing her first U.S. Women's Amateur, two-putted for par on the 13th to win that hole and put Creamer 5-down with five holes to go. McCurdy pitched her third to 9 feet at the par-5 14th and was conceded the birdie putt and the match.
Park and Huarte battled back-and-forth all day. Huarte, the 2004 NCAA Individual champion, saved par from five feet at the third to go 1-up. Huarte tripped to a bogey at the next to square the match.
Park again fell 1-down as Huarte rolled in a 6-foot birdie putt at the par-4 sixth. Huarte again faltered to a bogey, this time at the seventh to even the match.
Huarte birdied the ninth and Park the 10th to remain all square through 10. Huarte birdied the par-three 11th and climbed to 2-up with par on the 13th.
Park, last year's runner-up, took the lead thanks to poor play by Huarte. The 22-year-old Huarte stumbled to a bogey at the par-5 14th as her lead dropped to 1-up.
Park squared the match at the 15th with a par. Park stumbled to a bogey at the 16th, but it was good enough to win the hole and take her first lead. After the duo halved the 17th with bogeys, Huarte bogeyed the last to lose 2-down.