Cristie Kerr and Park Sung-hyun matched Lang's 65 to sit tied for third, three strokes behind Lang on seven under.
After a poor opening round of 75, world number one Lydia Ko got back to level after shooting three under. Thailand's Ariya Jutanugarn, hot on Ko's heels in the LPGA points race, struggled again at the SKY 72 Golf Club, posting a second straight 73.
Lang trailed overnight leader Lee by four after the opening round of the LPGA/KLPGA co-sanctioned tournament but a flawless round of five birdies and a chip-in eagle two at the 251 yard, par four 15th saw her claw back the deficit.
Lee fired back with a chip-in eagle at the same hole to retake the lead but made a mess of her approach to the last and finished with a bogey.
Lang's good form in Korea comes on the back of a dismal showing at last week's Fuban Taiwan Championship where she finished 13 over par -- 30 shots behind winner Jang Ha-na.
"That's golf," Lang told a news conference. "You got to just keep playing. I know I'm a good player. I tried my best and that definitely wasn't my week. You just got to move on."
Park, the number one Korea-based player, could have gone even lower than her 65 but her nine birdies were offset by a couple of untidy bogeys at the eighth and 11th holes.
After taking last week off, she had struggled to adjust to the pace of the greens in her opening round 72 but felt much more comfortable on Friday.
"I think I definitely adjusted to the speed of the greens," she added. "Yesterday during the first round I wasn't reading the distance quite right, and so the ball would hit the cup and fall out."
(Editing by John O'Brien)
