Wuesthoff, 17, along with Jennie Arseneault, Julieta Granada and Mari Chun, all shot 4-under-par 67 to take a three-shot lead over a group of five other golfers.
Jennie Lee, Tiffany Joh, Amanda Blumenherst, Paula Creamer and Ashley Freeman are all tied for fifth after shooting 1-under 70.
Maria Jose Uribe and In-Bee Park round out the top-10 following an even-par round of 71.
Wuesthoff, a New Jersey native, played 3-under-par over her final six holes to cap her first-round.
'Last year I played in front of people, and I was really nervous, but now I don't have that problem,' said Wuesthoff. 'I played in a couple of LPGA events so I was still a little nervous there, but in junior events it's OK now.'
Wuesthoff is appearing in her sixth U.S. Girls' Junior Championship. Last year, she came back from a five-hole deficit to win the title at Brooklawn Country Club in Fairfield, Connecticut.