Na Yeon Choi led a South Korean assault on the leaderboard at the Safeway Classic in Oregon.
Choi, a runner-up in this tournament last year, birdied seven straight holes to set a personal record and finished with a 6-under 65 to lead by two strokes over compatriot Grace Park.
"I'd like to go back to the 18th hole, really," Choi said of the double bogey on the final hole, the only blemish on her scorecard.
Park, who has withdrawn or been cut in 38 of her past 67 tournaments, has been beset by injuries over the past six years, from her neck to her back to her hip. She had back surgery one year ago, and the year before that, hip surgery.
"In the past that was my excuse and that was the truth," Park said. "But right now I'm healthy as I've been in 10 years."
Veteran Se Ri Pak is a further stroke back after a 68, tied with three others including a fourth South Korean player, M.J. Hur, Swede Anna Nordqvist and American Ashli Bunch.
Defending champion Ai Miyazato opened with a 1-under 70, equalling her best opening round performance since the U.S. Women's Open.
World No. 1 Yani Tseng opened with a 72 while Michelle Wie finished with a 3-over 74 after a double bogey-bogey finish.
Lisa Meldrum of Montreal, Alena Sharp of Hamilton and Charlottetown's Lorie Kane opened with 1-over 72s as did Paula Creamer and Brittany Lincicome.
LPGA rookie Stephanie Sherlock shot an opening round 73 as did Jessica Shepley of Owen Sound, Ont.
Adrienne White of Red Deer, Alta. shot 74 whlie Samantha Richdale of Kelowna, B.C., struggled to an 81.
Files from the Associated Press were used in this report