Miyazato ended the day at 8-under 134 through 36 holes at the rain-shortened event, one stroke ahead of Suzann Petterson and 16-year-old New Zealand amateur Lydia Ko.
Women's British Open champion and world No. 2 Stacey Lewis stormed into fourth place with a 67, two shots off the pace.
Miyazato, who led after the first round, bogeyed her first two holes but was able to get back on track and finish the round with four birdies, including the 18th.
"It wasn't a perfect round of golf, but I managed to put a score together and give myself a chance for tomorrow," Miyazato said. "I made a few key pars and tried to take advantage of good playing conditions."