Teenager Brooke Henderson claimed a tournament record score at the halfway stage of the LPGA Tour's Swinging Skirts tournament in San Francisco.
The Canadian, 17, recorded a seven-under-par 65 to take a two-shot lead from Choi Na-yeon at the halfway stage.
It gave Henderson a nine-under second-round total of 135, breaking Stacy Lewis's 2014 record by three shots.
"It's pretty cool," she said at the Lake Merced Golf Course. "This course is tough, and conditions are tougher."
Henderson is going for her lady Tour triumph and has needed to depend on backer exceptions to get into competitions in the wake of neglecting to win a card in qualifying school.
Her round incorporated six birdies and a bird despite the fact that she lurched to her first and final bogey of the week at the standard four fifth.
Inquired as to whether she was prepared to win her first huge competition, Henderson said: "I believe I'm prepared.
"Definitely, 17 is youthful. As you've seen with Lydia Ko and Lexi Thompson and even Jessica Korda, there are a considerable measure of extraordinary names that have possessed the capacity to do it. I'm trusting that I'm one of them."
To start with round pioneer and shielding champion Ko of New Zealand praised her 18th birthday with an even-standard 72 to complete tied for fifth.
South Korea's Choi checked a four-under 68 to seize sole ownership of second place.
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