Stacy Lewis holds a one-stroke lead at the half-way stage of the Swinging Skirts Classic in California after posting a second straight 69.
The American offset two bogeys with five birdies to reach six-under-par for 36 holes, as she chases a ninth career victory on the LPGA Tour.
Lewis, who has earned over $6.5m during her professional career, said: "We knew it was going to be a long day.
"I took it one shot at a time and tried to get the ball in the hole. That's what I tried to do.
"Get it in the hole as fast as I could. Fortunately, I was able to do that and make a couple putts."
For the second day in a row Lewis located 15 greens in regulation and her nearest challengers, with two rounds remaining, are New Zealand's Lydia Ko and Karine Icher of France.
Ko carded a 71 while Icher - the overnight leader - slipped to a one-over-par 73 in a round that yielded 15 pars at Lake Merced Golf Club.
Following her round at Daly City, she said: "It's a tough golf course.
"You can be quick in trouble or, if you're playing well, like yesterday I did think it goes pretty well - but today with the wind and the rain it was definitely a tough day."
The highest-placed Brit is Catriona Matthew who is tied-for-seventh following a three-under-par 69.
The experienced Scot is just four strokes off the pace following a brace of eagles on par-four holes.