Tina Barrett shot a course-record 9-under-par 63 to take a three-stroke lead in the LPGA event in Kutztown, Pa.
Barrett, who broke the Berkleigh record of 65 held by Laura Davies, Dale Eggling and Kelly Robbins, had nine birdies and hit all 18 greens in regulation in the lowest score of her career.
"If you would ever visualize a dream round, this would be it," Barrett said. "When I got a kick on the second hole, I figured it would be a good day, and I should take advantage of it."
She played the back nine in 5-under 30.
"I got more aggressive as the day went on, and I really started to feel good about myself," said Barrett, who won the 1989 Ocean State Open for her lone title in 12 years on the LPGA Tour.
Jean Bartholomew was second after 66. Meg Mallon and Sara Sanders opened with 67, and defending champion Hy Yung Kim was another stroke back along with Kristi Albers, Michele Redman and Maggie Will.
Host Betsy King shot 72, as did Amy Benz, who had a hole-in-one on the 143-yard 16th.