Chun In-gee moved two shots clear of the Evian Championship field on day two with a five-under par 66.
Having shared the lead with South Korean compatriot Park Sung-hyun after the opening round, Chun turned on the style on Friday to edge ahead going into the weekend.
Chun picked up shots at the second and third before a bogey at four dropped her to nine-under. After that there were no problems, though, as she made four further gains to finish the round at 13-under.
It was a day of mixed fortunes for Park, however, as she recorded six birdies and three bogeys, leaving her with a round of 68 and just off the pace in a tie for second with China's Shanshan Feng.
Ryu So-yeon is a further shot back on 10-under, but world number one Lydia Ko lost more ground as a 68 left her nine shots back in a tie for 13th.