Seventeen-year-old Lexi Thompson had a share of the clubhouse lead during the first round of the U.S. Women's Open on Thursday.
Thompson shot a 2-under 70 and was tied with Beatriz Recari of Spain and Ai Miyazato of Japan among early finishers.
Defending champion So Yeon Ryu finished with a 74 as players struggled in the nearly 100-degree (38 C) heat and high humidity at Blackwolf Run, a challenging 6,944-yard course in central Wisconsin.
Se Ri Pak, who won the Open at Blackwolf Run in 1998, shot a 72. Cheyenne Woods, Tiger Woods' niece, had a 75.
Top-ranked Yani Tseng has an afternoon tee time. She would become the youngest player to complete a career Grand Slam with a victory this weekend.
Beyond the challenges posed by Blackwolf Run's layout, plus the heat and humidity, players also had to stay focused during six-hour rounds.
''I didn't realize how slow it was going until I made the turn and it was three hours later,'' Thompson said.