Morgan Pressel fired a record-equalling eight-under par 64  to join Lee Mi-Rim atop the leaderboard after two rounds of the LPGA Kia Classic.
America's Pressel had eight birdies with no bogeys in a round that matched the course record at Aviara Golf Club.
Her 10-under par total of 134 tied her for the halfway lead with South Korea's overnight leader Lee, who signed for a second-round 69 that included six birdies and three bogeys.
They were one stroke in front of Americans Alison Lee, who climbed up the leaderboard with a 66, and Cristie Kerr, who carded a 68.
Spain's Maria Hernandez also posted a six-under 66 to grab a share of fifth place on eight-under 136. She was tied with Japan's Sakura Yokomine (67), South Korean Kim Hyo-Joo (68) and American Brittany Lang (68).
World number one Lydia Ko of New Zealand headed a group on 137, firing a two-under 70 for her 26th straight LPGA Tour round under par.
She was tied with world number three Stacy Lewis, who shot 69, and Alison Walshe, who carded a 67.
Pressel described her sparkling effort as "stress free."
"I hit almost every fairway, and I think I hit 16 or 17 greens and just had a chance for birdie on almost every hole," she said.
"I just hit it where I wanted to hit it today. It's been a while since I've been confident knowing where the golf ball would go, and so it was nice to swing freely out there today and have the result that I did," added the American, who won the most recent of her two LPGA titles in 2008.
"It's hard to win out here," Pressel said. "Sure, you would like to win more. But I've put a lot of time and hard work in."
Ko, the 17-year-old sensation who became number one in the world in February, has made winning look easy in her short, spectacular career.
Her 26th straight under-par round has her closing in on Swedish great Annika Sorenstam's LPGA record of 29 set in 2014.
"I don't know all the records and all the details on that, but like I always say, I'm going to try and have fun," said Ko, who has two wins worldwide this year. "If I play good golf and break some records, great."
Source: AFP