Bogeys on 15 and 17 have seen Lydia Ko drop down the leaderboard at the Swinging Skirts in San Francisco.

Ko had a share of the lead midway through her back nine of her second round, at seven under, but has now dropped to five under par and a tie for 4th.

Japan's Haru Nomura has a three shot lead at nine under with a handful of holes to play, with Australia's Minjee Lee and Korean So Yeon Ryu tied for second.