Tseng's last victory came at the Kia Classic, but she was in prime position to end the drought after finishing the day at 18-under-par 198 -- a tournament record for three rounds.
Sharing second at 15-under were Suzann Pettersen (70) and Pornanong Phatlum (71).
Second-ranked Stacy Lewis was among four players knotted for fourth at 14-under thanks to a round of 7-under 65.
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