The South Korean, who held a one-shot lead after 18 holes, completed two rounds at Highland Meadows Golf Club at 11-under 131, two clear of Christina Kim (67), Alena Sharp (68) and Inbee Park (66), all of whom finished at 9-under 133.
Jiyai Shin, the former world's top woman golfer, registered a 1-under 70 and ended up as part of gaggle of eight golfers tied for 11th at 5-under 137.
Missing the cut was 2008 Jamie Farr champion Paula Creamer, who was playing in her first tournament since undergoing thumb surgery four months ago.
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