Teenager Brooke Henderson hit a hole-in-one as the world number four posted a four-under-par 67 to lead the KPMG Women’s PGA Championship by two shots.
The Canadian aced the par-three 13th in the second women’s major of the year – at Sahalee Country Club in Washington.
Christina Kim and Kim In-kyung are tied second after opening rounds of 69.
New Zealand’s world number one Lydia Ko, 19, is level par as she chases a third successive major after winning the ANA Inspiration in March.
Thailand’s Ariya Jutanugarn, who has won her last three LPGA tournaments, is one of six players who hit one-under-par 70s in the second women’s major of the year.
England’s Melissa Reid and Jodi Ewart Shadoff are five shots off the lead after opening rounds of 72, while compatriot Charley Hull, who finished second to Ko at the ANA Inspiration, is a shot further behind.
Scotland’s Caitriona Matthew is in danger of missing the cut, currently projected at four over, following a five-over par 76 that included a triple-bogey six at the par-three 17th.
South Korean world number two Park In-bee, the three-time defending champion, shot a one-over 72 on Thursday.
Park, 27, has now qualified for the LPGA Hall of Fame after completing 10 years on the Tour, becoming the 24th and youngest member since compatriot Pak Se-ri.
“It feels surreal. I have been dreaming of myself being in the Hall of Fame so many times,” Park said.
“This truly feels amazing. I’m really going to enjoy today and there are so many people that helped me get here.”
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