They were seven-under par when play was halted in semi-darkness on an unusually cold day that prompted many players to wear several layers of clothing for protection from the biting northerly wind.
Ko and Jang had a one-stroke lead over five players, including long-hitting American Lexi Thompson (seven holes), while 2014 U.S. Women's Open champion Michelle Wie (12 holes) was four shots behind.
The third round will resume on Saturday at 7.30am, with the final round to start immediately afterwards.
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Ko lamented some birdie putts that did not drop.
"I've just got to stay positive with the putter, but sometimes you just have to take what's going, and it's not like every single one of them is not dropping," the South Korean-born Kiwi teenager told reporters.
On the seventh green, Ko feared her ball had moved after she had addressed it for a tap-in.
Officials subsequently viewed TV footage of the incident, but detected no movement.
"You just want to make sure before you putt it out," said the 10-times LPGA winner.
"I've had times where it has moved before, so I just wanted to clarify things, especially when it's that dark.
"I just want to make sure so that there are no further problems later on and then I can sleep peacefully."
Jang, meanwhile, said she was feeling "very confident" about her game as the 23-year-old plots a first LPGA victory, after four runner-up finishes last year.
(Reporting by Andrew Both in Cary, North Carolina; editing by Sudipto Ganguly)
