Miyazato sits on 11 under par, leading by two shots from South Korea's So Yeon Ryu with Cristie Kerr and Inbee Park a further shot behind.
Joint first round leader Sydnee Michaels had been a shot back with two holes left to play, but dunked her tee shots into water on both the 17th and 18th holes to slip back into a share of fourth at seven under par, alongside world number one Yani Tseng and American star Paula Creamer.
Miyazato has two recent second places to her name, and is seeking to go one better.
"I have so much good experience the last four or five events," she said. "But I don't know how much closer to win the tournament. I try to focus on my golf game, one shot at a time."
Tseng has three victories so far his season but has not won in the past five months, yet she is confident that Pumpkin Ridge will give her a chance to come through in the final round.
"I'm (four) shots back, so on this course, you can make a lot of birdies here," she said. "I feel I'm getting back. I can get back slowly. I don't have to win this week. I can play well tomorrow and maybe next week I'll win, but you never know."