Miyazato, a two-times winner on the LPGA Tour this year, bogeyed the par-5 second hole but hit four birdies in a five-hole run to finish the front nine.
Four more birdies came on the back nine but she blotted her copybook with a missed putt on the final hole.
"I've been dealing with my putting since last month and it just didn't go in," Miyazato said. "But I just say to myself, 'Just be patient and it's going to go in some day.'"
US Women's Open champion Na Yeon Choi is second, one shot behind.
Joint first-round leader Sun Young Yoo incurred a one-shot penalty for not raising her arm high enough on a drop at the 14th hole, putting her three back.
Stacy Lewis, who will receive the LPGA player of the year award at a gala dinner on Friday, had a 72 to put her eight shots back.
"Pretty frustrating," Lewis said. "My game just hasn't been sharp the last two days. Just been a little off putting, a little off chipping, a little off the iron game. You can kind of see it in the scores. Just haven't quite got things going."
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