South Korean Jenny Shin shot a bogey-free seven-under-par 65 to take a one-stroke lead after the second round of the Kia Classic in southern California on Friday.
Shin made a hot start with five birdies in the first eight holes on the demanding Aviara course in Carlsbad.
She posted a 10-under 134 halfway total, with New Zealander Lydia Ko (67) and American Brittany Lang (68) equal second on nine-under.
The 23-year-old has not won an LPGA event since joining the tour in 2011, but has 18 top-10 finishes and thinks she is "ready" to break through.
"I feel like in every aspect of the game I'm improving just a little bit and hopefully it will come together sometime this year," Shin told reporters.
Ko sounded confident of making a weekend charge for what would be her 11th career LPGA victory on a course considerably more difficult than last week's venue in Arizona, where she shot 22-under but still finished five strokes behind the winner.
"Last week was crazy. You just couldn't make enough birdies," she said.
"This week is definitely different. The course plays a little longer and it's a little tighter off the tee and with the rough being really lush, that's another huge component. The rough is rough.
"I didn't strike the ball as well as I did yesterday, especially on my back nine, I had to make up-and-down from a few places."