Ai Miyazato, who was among the four overnight co-leaders, struggled in windy conditions and dropped to ninth with a 5-under-par 139 total, five strokes off the pace after the second round of the Kia Classic on Friday.
Miyazato got off to a bogey-free start at the Aviara Golf Club and opened the back nine with birdies on Nos. 2 and 5, but then missed a three-yard par putt three times to finish with an even-par 72.
"I persisted. I give myself a passing grade," said Miyazato.
"I'm feeling a good mental-technique balance. I hope to keep playing this way for the next two days."
Jenny Shin of South Korea took the sole lead after a round of 65, followed by Korean New Zealander Lydia Ko and American Brittany Lang tied for second on 135.
Harukyo Nomura carded six birdies and three bogeys for a second-round 69 to join Miyazato and three others for a share of ninth place.
"I feel good being in a good position. I still have two days to go so I'm going to aim for one of the top spots," Nomura said.