Su Oh heads the Australian challenge after round two at the LPGA Classic in Grand Rapids, seven shots off the pace set by teenager Brooke Henderson.
The Canadian 19-year-old carded a four-under par 67, despite bogeys on her final two holes, to lead by two shots at 12 under.
Henderson had seven birdies and three bogeys at Blythefield Country Club on Friday.
"This week seems to be a turnaround week and hopefully I can just finish strong the next two days," Henderson told lpga.com.
Fellow major champion Lexi Thompson fired a 68 to be tied for second with Spain's Carlota Ciganda (64) and Korean Mi Jung Hur (66) at 10 under.
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Moriya Jutanugarn, Ariya Jutanugarn's older sister, is fifth at nine under after a 66.
Ariya Jutanugarn, playing her first event as the No. 1 player in the world, was tied for 30th at four under.
New Zealand's Lydia Ko, world No. 2 after an 85-week run at the top, was tied for 14th at six under after a 71.
Oh backed up her first round 67 with a 70 to be at five-under par in a share of 20th place, while countrywoman Sarah Jane Smith is a shot further back after back-to-back rounds of 69.
Aussie trio Karrie Webb (68,76), Katherine Kirk (70,71) and Sarah Kemp (70,72) missed the cut.
