Five players are two strokes back at 71 and 12 more shot 72 Thursday.
Tseng, the World No. 1-ranked player and a two-time defending Australian Open champion, opened with a bogey but had four birdies in a six-hole stretch. She briefly reached 4-under with a birdie at the eighth hole but a bogey at No. 9 -- her closing hole -- left her in second.
Lewis, playing the back nine of the Royal Melbourne Golf Club first Thursday, had a bogey at the 11th hole but answered with four birdies in the next six holes before closing the side with a bogey at 18. She pulled into a tie for the lead with birdies at Nos. 6 and 8.
Kemp also played the second nine first and had 10 pars and a birdie -- at the 14th -- before posting back-to-back birdies at 3 and 4. She took a share of the lead with a birdie at the seventh hole.
This is the first year the Women's Australian Open is associated with the LPGA.