SPRINGFIELD, Ill., July 18 (UPI) -- Christina Kim maintained her one-stroke lead with a 4-under-par 68 in the second round of the LPGA's State Farm Classic in Springfield, Ill.

Kim shot 9-under 63 in Thursday's first round and her 68 on Friday gave her a 36-hole total of 13-under 131.

During Friday's round, she negated a bogey at the par-5 sixth hole with five birdies.

"Today was just personally quite a struggle I thought actually," Kim said. "It seemed slightly more difficult."

Former teenage phenom Michelle Wie continued her surge with a 7-under 65 and at 12-under 132, shares second place with Yani Seng (66), Sherri Turner (66) and Ji Young Oh (66).

Wie's 65 was her best single-round score since a 66 at the 2006 Evian Ladies Masters.

"It helps to have a good bounce here and there, you know," Wie said. "But overall, I felt like my game was pretty solid."

Defending champion Sherri Steinhauer (71) missed the cut with her two-day total of 2-over 146.