Sticking to her mantra of staying patient, Jang hit four birdies and an eagle in a blemish-free round on the demanding Serapong Course to put herself in prime position to mount a challenge for a second win in five starts this year.
Lee was also bogey-free and registered her fifth birdie of the day on the par-five 18th to sign for a five-under-par 67 that put her alongside Jang on eight-under for the $1.5 million restricted-field event.
The leading duo sit a stroke clear of Norway's Suzann Pettersen and Pornanong Phatlum of Thailand in a share for third on a packed leaderboard that has the top 19 players separated by just four strokes.
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Jang claimed her first LPGA title at the Coates Golf Championship in Florida last month, backed it up with two top-10 finishes and continued to pepper the flag with her approach shots on Friday to give herself plenty of birdie opportunities.
"Today I just told myself to be patient and not to think about the score, other players and the golf course and it seemed to make it easy for me," she said in a post-round interview.
"I have two more days, so I need more concentration but I think I can do it."
The 23-year-old cut her teeth on her domestic tour but has already made history in her second year on the LPGA when she became the first golfer on the circuit to hit a hole-in-one on a par-four at the Pure Silk-Bahamas LPGA Classic.
Lee has struggled to replicate the form that led her to two victories in her rookie season in 2014 but the 25-year-old has just a single bogey on her card after 36 holes and her strategy for the weekend could not be simpler.
"I'm just going to try and hit it straight, straight, straight and then make, make, make," she said, while admitting that her short game was key to her improved performance this week.
Defending champion and world number two Park In-bee had a day to forget, however, after she started her round with three bogeys in four holes but recovered slightly to sign for a one-over-par 73 that left her five off the pace in a tie for 20th.
Her main rival Lydia Ko fared even worse, the world number one carding a two-over-par 74 to fall into a tie for 41st at one-over, two adrift of American Lexi Thompson, winner of last week's event in Thailand, who signed for an even-par 72.
(Reporting by John O'Brien; editing by Sudipto Ganguly)
