Miyazato finished second in this tournament last year and turned in a strong back nine at the Wildfire Golf Club to lead by two.
She was 4-under for the day when she came to the par-3 14th hole, where she made a birdie. Miyazato then eagled the par-5 15th and birdied the next two holes as well to jump to the top of the leaderboard.
Jee Young Lee was alone in second at 65, which had been the old course record.
Defending champion and world No. 1 Yani Tseng shot a 2-under 70 and was tied for 39th.
This is the first LPGA Tour event to be played in the United States this year after the circuit conducted a series of winter events in Asia.