The 19-year-old from Okinawa had five birdies and three bogeys in her 70 to reach 15-under par with Swedens Cecilia Ekelundh making up ground to 12 under after a faultless 5-under-par 67.
Australias Karrie Webb is in third place alone on 11 under par, while Veronica Zorzi from Italy sits a shot further back on 10 under par after a round of 69.
Im very happy with my position, said Miyazato, who won five times in her rookie season on the Japanese Tour in 2004.
I havent felt the pressure over the last three days and Ill carry on the way I have been playing tomorrow.
Ekelundh, who won the Ladies Open of Portugal last year, vowed that she will learn form her experience of winning last season and give it all in the final round here on Sunday.
There was a lot of pressure then and I remember being very nervous but I know how to do it. This is a bigger tournament, but Im really looking forward to it.
But Webb lurks ominously looking for her fifth ANZ Ladies Masters title. The 30-year-old from Ayr in Queensland knows she will need to be in top form, but she will have the opportunity to put the pressure on playing with Miyazato in the final group on Sunday.
Webb has improved each day with rounds of 70, 68 and 67 and knows she will need to pull out a special round to fend off Miyazato.
I kicked into another gear on the back nine and really started to focus, said Webb, who came home in 31 strokes, making four birdies on her last seven holes.
Im not complaining but I could have easily been a couple of shots lower today and Ill have to go low tomorrow because I would not expect Miyazato to come back to the field.
Sitting in a three way tie for fifth spot is Swedens Maria Hjorth, who had a 71, Rachel Hetherington from Australia and Englands Kirsty S Taylor, who was slightly disappointed with a 3-under 69, especially after a fast start when she was 4 under after the first seven holes.
Coming home in level par 36, Taylor felt she had let an opportunity slip.
I let it go big time, said Taylor, who played with Webb for the first time in her career.
I would have liked that to be a little better than that, but Im hitting the ball well, I just need to hole a couple more putts. I loved playing with Karrie today, especially with a big gallery and that really gets me going and Im excited about tomorrow.