Tseng, the No. 1 player in the world and Taiwan native, finished 54 holes at 10-under 206 and is two strokes clear at Sunrise Golf & Country Club.
Anna Nordqvist, one of the second-round co-leaders, managed a one-under 71 and is alone in second at minus-eight. Azahara Munoz, the other leader at the midpoint, shot an even-par 72 Saturday and is third at seven-under 209.
Tseng, who shared the first-round lead on Thursday, will be chasing her seventh LPGA Tour title of 2011 and her 12th all time on the circuit.
MORE TO FOLLOW.