Ko on top in San Francisco

Ko hit six birdies and a bogey on the par-four 11th during her fantastic opening round. 

Ha Na Jang, Juli Inkster and P.K. Kongkraphan are all right on Ko's heels as they carded a 68 in their first round. 

Jang hit eight birdies and four bogeys, Inkster got six birdies and two bogeys and Kongkraphan ended up with four birdies, two bogeys and an eagle on the par-five 14th. 

Sitting one stroke behind them is Morgan Pressel, Caroline Hedwall, Stacy Lewis and Na Yeon Choi. 

Pressel hit six birdies and three bogeys, Hedwall sunk seven birdies and four bogeys and Lewis nailed six birdies, four bogeys and an eagle on the par-four 11th. Choi meanwhile finished with six birdies and three bogeys. 

World number two Inbee Park did not enjoy a successful first round as she hit a 73, which included three birdies and four bogeys.