Ochoa, who had six birdies in the second nine, is 1-stroke up on Sun Ju Ahn, Candie Kung and Angela Park, who turned in 6-under 66s Thursday. Another five golfers are at 5-under 67.
Ochoa birdied the first hole Thursday but then had eight consecutive pars.
"I had a slow start," she said. "I made birdie on the first hole and didn't give myself a lot of birdie chances after that," Ochoa said. "I got some confidence from the putts on 10 and 11, and started feeling good over the ball. I finished making six birdies on the back, so I have no complaints. I'm really happy."
After the birdies at Nos. 10 and 11, Ochoa parred No. 12. She had another birdie at 13, a par at 14 and ran off three more birdies from 15-17 to get to 7-under. A par 5 at the 18th left her with a 30 on the back nine.