The Japanese shot a solid two-under-par 70 in windy conditions today [Saturday] to move clear of the chasing pack on 10 under.
Miyazato, a seven-time LPGA Tour winner, had started the day level with Spain's Azahara Munoz who was in a share of second place with Cristie Kerr.
Munoz was one-over for the day, combining four birdies with five bogeys, to slip back while Kerr produced a round of 71 to give herself hope
World number one Yani Tseng was looming on six under after the Taiwanese shot the day's equal-best round of 69.
US Open champion So Yeon Ryu also went around in three under to join Tseng four shots off the pace.