Kim, who won this year's Ginn Clubs & Resorts Open, shot a 5-under 67 in round three, while Lang, who tied for second last year as an amateur at the U.S. Women's Open, posted a 3-under 69. The pair is knotted at 10-under-par 206.
Jang wasted little time in breaking into red figures. She knocked a 7-iron to 6 feet to set up birdie at the first, then drained a 15-footer for birdie at the second.
The reigning Women's British Open champion seemed to be in trouble at the 161- yard, par-3 fifth. Jang's s6-iron tee ball missed the green left, but she chipped in from 15 yards for her third birdie of the round.
Jang played steady golf around the turn with all pars until the 12th hole. She hit a pitching-wedge to 10 feet and rolled in the birdie try at 12 to reach 9 under par for the championship.
At the par-3 15th, Jang once again hit a solid pitching-wedge shot. She holed her 15-foot birdie putt, then added a 9-footer for birdie at 16 to take sole possession of the lead.
'I think I missed one fairway,' said Jang. 'My putting was really good and the driver was the key I think. I'm very good right now.'
Jang has not won since her major triumph last year, but has posted six top-10s in 2006. A few weeks back at the LPGA Corning Classic, Jang had the lead on the final day, but played poorly and tied for seventh place.
'I was a little bit disappointed and I want to do a better job tomorrow,' acknowledged Jang. 'I just want to keep thinking about golf more and I didn't take it last time when I was leading at Corning. Everybody is playing good so we need to hit a low score.'
As for the win last year at Royal Birkdale, Jang has a newfound confidence.
'I think everything changed,' admitted Jang. 'My life, my golf, everything changed. Winning that makes it comfortable and makes it like, 'OK, I can do it.''
Kim collected her first birdie of the round at the second hole when her 9-iron stopped 10 feet from the hole. She holed out a sand-wedge from 65 yards for an eagle at the fourth and Kim recorded another birdie at eight when she converted a 7-footer.
At the 12th, Kim hit an 8-iron into the wind, but got the ball to stop 6 feet from the flag. She cashed in on the birdie putt to get within one of first place.
'Today, I missed a little bit and missed a couple of putts,' said Kim. 'But now I'm very happy with my score today.'
Lang had an up-and-down round as she made the turn at even-par thanks to one birdie and one bogey. She dropped another shot at the 10th when she three-putted from 30 feet, but reclaimed the lost stroke at the par-5 11th.
Lang ran home a 4-foot birdie putt at the 12th and birdied 15, but bogeyed the 16th when she missed a 9-footer for par. She closed her round in style with a tap-in eagle at the 17th and made a strong par at the last after her drive landed behind a tree.
Next up is win No. 1 for the former Duke University standout.
'It's going to be fun,' said Lang. 'I have never been in this position. I'm excited. I'm just going to go out and play aggressively and play hard.'
Marcy Hart (66), Soo Young Yoo (66), Silvia Cavalleri (68) and Wendy Ward (70) are knotted in fourth place at minus-8. Former U.S. Women's Open champion Hilary Lunke (65), Julieta Granada (67), Sherri Steinhauer (69), Aree Song (69) and Rachel Hetherington (71) share eighth place at 7-under-par 209.
Overnight leader Shi Hyun Ahn struggled on Saturday. She shot a 3-over 75 and is part of tie for 19th place at 5-under-par 211.