Jang birdied her final four holes to reach 11 under with seven holes left in the second round. She opened with a 4-under 68 on Thursday at Desert Ridge.
Fellow South Korean player Hyo Joo Kim was a stroke back.
Kim played 30 holes Friday in the tournament that fell behind Thursday when rain delayed the start four hours. She completed a 65 in the first round and had 69 in the second.
Stacy Lewis and Kim Kaufman were 9 under.
Lewis, the 2013 winner, also played 30 holes. She opened with a 64, making seven birdies in a nine-hole stretch to take the first-round lead, and added a 71.
Kaufman bogeyed her final hole of the day, the par-4 12th.