The top-ranked Tseng, the LPGA Championship and Women's British Open winner, leads the tour with four victories this season and has seven overall wins this year.
"I think it's hard to not have pressure because, I mean, for sure I've got pressure tomorrow, defending champion and in the lead," Tseng said. "The kind of thing's going to be a little pressure, but I just want to enjoy that pressure. I know tomorrow, first couple holes going to be nervous. If I were not nervous, that would be a little weird, so I mean, I care."
"I was kind of frustrated," Lewis said. "I left a lot of putts out there. My speed was just a little off and my lines were a little off, but still it was a good enough round that it kept me in it for tomorrow."
Michelle Wie missed the cut with rounds of 78 and 72.
Tseng had six birdies and two bogeys on the Pinnacle Country Club course. She nearly aced the 160-yard 15th hole, hitting to 2 feet to set up a birdie. She played her back nine in 32.
"I worked on my tempo on the back nine," Tseng said. "I got a little too fast with my tempo, but I just keep to myself, keep focused, and actually back nine I got really lucky. I had a good bounce on No. 8, good bounce on No. 4 or 5, and I have a great up and down on par 3, so those three shots were important."
Yang is winless on the LPGA Tour. She eagled the par-5 seventh.
"Everything was good today," Yang said. "I was hitting the ball solid and hitting the putts solid. You know, from tee to green, I was playing good. I'm really happy about my game."
"I play to win, that's for sure," Creamer said. "I'm out here trying to win every week that I can. It hasn't been the stellar year that I wanted it to be, but I've been overcoming a lot of things. I feel really good about where I am."
Jaclyn Sweeney had a hole-in-one on the par-3 sixth, but missed the cut with rounds of 77 and 71. Pernilla Lindberg aced the 11th Friday.