Defending champion Cristie Kerr ran into problems down the stretch to leave Soo-Yun Kang and Jee Young Lee atop the leaderboard through Friday's second round.
Kang shot a 6-under 66 and Lee had a 67 to share the top spot at 11-under 133 at the tournament's midpoint.
'We are very friendly,' Kang said of the relationship between the 32 South Koreans on the LPGA Tour. 'After we finish a round, we go to dinner sometimes, and we drink. We talk a lot.'
They have a lot to discuss. No fewer than 12 South Koreans are among the top 30 on the tour money list. They've already won nine times this season.
Lee said there is a natural rivalry between the players but all is forgotten off the course.
'I cannot deny the competition among Korean players,' she said. 'But on the other hand, I know that golf is actually against one's self.'
Se Ri Pak opened the door for South Koreans with four wins in 1998. Since then they have made themselves right at home.
Pak has collected five major championships among her 23 victories, while Mi Hyun Kim, Hee-Won Han, Jeong Jang, Birdie Kim and Gloria Park have all made names for themselves. Seon-Hwa Lee is 11th on the money list and the frontrunner for rookie of the year, with pressure from Lee, who is 22nd.
Sweden's Mikaela Parmlid shot her second consecutive 67 and was a shot back along with Colombia's Marisa Baena, who had a 65 to match the low round of the day with two more Koreans, Joo Mi Kim and Young Kim.
Things finally came together for Parmlid.
'I've been playing amazing the last three weeks really, and I haven't putted well,' she said. 'So finally I talked to my teacher right before the tournament, he helped me out a little bit and the putts started dropping.'
Brittany Lincicome, Lorena Ochoa and Karrie Webb each had a 68 to stand two strokes back at 135. Paula Creamer had a double-bogey on the second hole but mustered her second 68 and was at 136 along with Joo-Mi Kim (65), Stacy Prammanasudh (70) and Ai Miyazato (68).
'You walk away with a double and you're not really feeling too good about yourself,' Creamer said. 'But I fought back and had three birdies in a row and then birdied No. 9. Things happen like that and you just have to overcome it and come back.'
Kerr was the hottest player on the course for most of the day but faltered at the finish. She three-putted the 17th for bogey and then pulled her second shot into a small creek on the par-4 18th. She had to settle for a double that capped a 67 and left her at 137.
'I just made an absolutely horrendous swing on the last hole,' she said as she hurried to the fitness trailer for therapy on a sore neck. 'All I had to do was hit it to the right side of the green and it would kick down to the hole. It was an awful, awful shot.'
Even after giving away three shots to par on the final two holes, she was only four back of the leaders.
'It's really hard right after I walk off the green to be positive about it but I'm sure by the time I relax and get my neck worked on, I'll look back on the overall day instead of the finish,' she said. 'But right now I'm furious.'
Prammanasudh, Lee, Katie Futcher and Kristal Parker-Manzo shared the first-round lead at 66. Futcher, a rookie, came back with a 73 while Parker-Manzo, who said she would retire after this tournament, faded to a 76.
With the greens holding, the leaders vowed to continue firing at pins -- possibly leading to the lowest 72-hole scores of the year on tour.
'If the greens stay receptive, it could be a possibility that 20-under could win the tournament,' Baena said.