Lindsey Wright (71) and Sun Young Yoo (69) are third at 6-under, while Hall of Famer Se Ri Pak (69) is three strokes back in fifth midway through the only major she has never won.
Tseng extended her thorough domination of the women’s game with another relentless round of long drives and steady putting. After finishing the opening round two strokes back, she’s leading for the ninth time in the LPGA Tour’s past 10 rounds.
Pak shot 69 to move to 5-under. Karin Sjodin (67) and World No. 2 Na Yeon Choi (67) joined Pak in fifth.
EUROPEAN TOUR: In Sciacca, Sicily, John Daly had five birdies and an eagle for 5-under-par 67, finishing two shots off the leaders at the Sicilian Open.
Daly, 46, trailed six players, including first-round leader Peter Lawrie, who shot 72.
Lawrie was joined at 8-under by Jamie Donaldson (71), David Lynn (69), Pelle Edberg (66), Maarten Lafeber (68) and Simon Wakefield (67).
Defending champion Raphael Jacquelin (73) and teenager Matteo Manassero (72) failed to make the cut.
Rich Beem shot his second 69 to move alongside Daly at 6-under.