Tseng collected birdies after two of the round's three rain delays -- on the 10th and 14th holes -- and followed up with another birdie on the 15th to establish the winning margin.
Tseng parred the last three holes to hang on for her 14th career LPGA title at 18-under-par 270.
Second-ranked Na Yeon Choi also fired a 68 to finish one shot behind at minus-17, joined there by former No. 1 Ai Miyazato (69) at J.W. Marriott Phoenix Desert Ridge Resort & Spa.
Claiming sole possession of fourth place at minus-15 was Jennifer Song, who carded a 7-under 65.