Sweden’s Sophie Gustafson led the Longs Drugs Challenge by two shots after shooting a first round total at 65 for seven under par on the Blackhawk Country Club course in Danville, California.
Gustafson had eight birdies and one bogey to lead by two from Sophia Sheridan, Angela Stanford and Na Ri Kim who all shot 67.
Lorena Ochoa had five straight birdies in a round of 68, a score matched by 2006 winner Karrie Webb, Shanshan Feng and Kyeong Bae.
Money list leader Jiyai Shin had a 72 and defending champion In-Kyung Kim struggled to a 73.
Thirteen-year-old Casie Cathrea, playing on a sponsor exemption after winning a qualifier on Monday, made a hole in one on the 155-yard 12th and finished with a 74.