Na Yeon Choi fired her second straight 5-under 67 on Friday, and that gave her a 1-stroke lead after two rounds of the Women's British Open.
Choi, the 2012 U.S. Women's Open champion, finished 36 holes at 10-under-par 134. She has seven LPGA Tour titles, but hasn't won since the end of last year.
Miki Saiki fired a 6-under 66 to jump into second place at minus-9.
First-round co-leader Morgan Pressel managed a 2-under 70 and dipped into third place at 8-under 136 on the Old Course at St. Andrews.
Suzann Pettersen and Jee Young Lee both shot 67 on Friday to move into a share of fourth at minus-7. They were joined there by Nicole Castrale (70). Mikaela Parmlid carded her second straight 69 to end two rounds alone in seventh at 6- under 138.
World No. 1 Inbee Park, who has won the season's first three major championships, stumbled to a 1-over 73 on Friday. She fell eight strokes off the pace at 2-under-par 142.
Park, who has won six titles in all this season, stumbled out of the gate with a bogey at the first. She atoned for that error with a birdie on the sixth, and parred her next three holes to play the opening nine in even-par.
Around the turn, Park faltered to a bogey on the 10th. She got that back thanks to a birdie at 12, but she stumbled to a bogey at 13 to again dip to minus-2.
Park, last year's runner-up, bogeyed the road hole, No. 17, but closed with a birdie at the last to end eight back
"When you experience something big like this, some kind of big pressure like this, you're just really not afraid of any kind of pressure. How can it get bigger than this? If you experience something like this, you're just ready to go and ready to experience something, anything's going to be less than this," said Park of her chance at winning a fourth straight major.
Choi, who was runner-up at the HSBC Women's Champions earlier this year, got her round going with a birdie on the third. At the fifth, she poured in a birdie putt from just over 40 feet out to move to 7-under.
The 25-year-old made it two in a row as she birdied the sixth, but Choi gave that back as she stumbled to a bogey at No. 7. She quickly erased that mistake with a birdie at the par-3 eighth.
Choi parred three in a row from the ninth. She birdied the 12th to move to minus-9. After a pair of pars, Choi birdied the 15th from 35 feet out.
"The weather wasn't good. It was very hard. But my focus was very good and my caddie helped me a lot," said Choi, who played in the worst of Friday's weather. "I had a daily goal every day, so I just tried to stick with the goal. I just try to play one shot at a time and I think that's why I had great results."
Saiki wrapped birdies at the first and third around a bogey at the second. Over the next four holes, she flew into contention. At the fourth and seventh, Saiki holed out for eagle on both holes to jump to minus-8.
"First time (I've done that). The first one on No. 4 was 127 yards to the hole and a shot with an 8-iron. The one on seven was 108 yards to the pin," Saiki said describing her eagles.
The 28-year-old, whose final-round 67 was the low round of the championship at St. Andrews in 2007, birdied the ninth to shoot 6-under 30 for the opening nine holes.
Saiki played the back nine in even-par with a birdie at 14 and a bogey at 16.
Pressel had a steady round with birdies at three and 10 to go with 16 pars.
"I played very well today. Didn't really put myself in any trouble. I only had one par putt of maybe about six or seven feet on 11, that wasn't a tap-in," Pressel stated. "There's a lot of birdie putts out there. I gave myself a lot of chances and they were scaring the hole, but just didn't go in. On the last hole, I was ready to give a big fist pump, but it missed on the low side."
Camilla Lennarth, who shared the first-round lead with Pressel, struggled to a 10-over 82 and missed the cut by three strokes.
NOTES: Defending champion Jiyai Shin carded a 72 on Friday and is tied for 30th at minus-1 ... The cut line fell at 1-over 145, which tied the lowest cut in championship history ... Sixty-nine players moved on to the weekend ... Among those that missed the cut were 2010 & 2011 champion Yani Tseng, Laura Davies, Ai Miyazato, Lexi Thompson and World Golf Hall of Famers Karrie Webb and Juli Inkster ... The U.S. Solheim Cup team has the top eight places locked in after the event .... The top seven are locked in with Stacy Lewis, Paula Creamer, Cristie Kerr, Angela Stanford, Brittany Lincicome, Lexi Thompson and Jessica Korda. Brittany Lang is eighth, but missed the cut and can be bumped out by Lizette Salsa, Gerina Piller, Pressel or Michelle Wie.