Yani Tseng carded a five-under 67, while Ai under 66 Saturday as the duo finished 54 holes tied for the lead at the LPGA Founders Cup.
Tseng and Miyazato finished three rounds at 14-under-par 202. Tseng earned her 13th tour title earlier this year in Thailand, while Miyazato picked up her seventh win last year at the Evian Masters.
The battle on Sunday won't just be between the current world No. 1, Tseng, and former No. 1, Miyazato. World No. 2 Na Yeon Choi posted a 67 of her own and is one stroke off the lead at minus-13.
I.K. Kim and Inbee Park both managed three-under 69s in the third round. Kim is alone in fourth at 11-under-par 205 and Park is one back at minus-10 on the Wildfire Golf Club at JW Marriott Phoenix Desert Ridge Resort & Spa.
There is bad weather in the forecast for Sunday so the seven players tied at minus-nine aren't out of the picture either. Among those are the third, fourth and sixth ranked players in the world.
Tseng started the round with a one-stroke lead, but even with a hot start, her margin only grew to two.
The 23-year-old birdied each of the first three holes to get to 12-under. Tseng was two clear of Kim at that point.
Tseng rolled in a short birdie putt on the seventh to extend her lead to three. After three straight pars, she stumbled to a bogey on the 11th and was suddenly just one clear of Miyazato.
Playing in the group ahead of Tseng, Miyazato had a pair of birdies on the front nine. She birdied the par-five 11th to move to 11-under, where she was one back.
Miyazato dropped in back-to-back birdie efforts from the 14th to join Tseng at 13-under. Tseng got there when she birdied the par-three 14th. Miyazato briefly took a one-stroke lead as she converted her third consecutive birdie try on the 16th. She parred the final two to end there.
"No, it wasn't easy out there because of the wind, but I just took it one shot at a time," Miyazato said in a televised interview. "I've been trying to keep the same swing tempo with every club. It's not really easy to do in the wind though."
Tseng poured in a 25-foot birdie putt at the 17th to join Miyazato atop the leaderboard. Tseng missed an eight-foot birdie try at the last that would have given her the third-round lead by herself.
"I played so good today. I hit lots of great shots out there and I missed a few short putts," Tseng stated in a television interview. "Those long putts on 17 and on three, those are the ones I'll remember."
Pettersen, Kerr and Creamer were joined in sixth place by defending champion Karrie Webb (70), Hee-Won Han (68), Hee Kyung Seo (69) and reigning U.S. Women's Open champ So Yeon Ryu (68).
NOTES: At one point early in the round, there were 12 players tied for second place...Miyazato and Kerr both shot 66 to match the low round of the day...Players will be in threesomes off the first and 10th tees again on Sunday with inclement weather in the forecast.