Miyazato, tied for the first-round lead with Sydnee Michaels after a 65, had an 11-under 133 total on Pumpkin Ridge's Ghost Creek Course.
South Korea's So Yeon Ryu, the Toledo Classic winner last week, was second after a 68. Ryu and Miyazato, winless in her four seasons on the LPGA Tour, will be paired together again Sunday after playing in the same group the first two days.
Cristie Kerr and Inbee Park shot 70 to reach 8 under, and Michaels had a 72 to join top-ranked Yani Tseng and Paula Creamer at 7 under. Tseng had a 67, and Creamer shot a 69.
"I have so much good experience the last four or five events," Miyazato 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."
She was asked if she's ready to win.
"I'm always ready," she said.
Miyazato must fend off Ryu, who closed with a 9-under 62 last week in Ohio to tie the LPGA record for lowest final-round score for a winning player. Ryu is 29 under in her last six rounds of competition, all six rounds in the 60s.
"(Miyazato) is ready to make a win. The problem with golf is it's quite a
Tseng leads the tour with three victory, but hasn't won since March and missed the cut in three of her previous four tournaments.
"I'm (four) shots back, so on this course, you can make a lot of birdies here," Tseng 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."
Kerr, who won
"Typically, the winner of this tournament shoots a low round on Sunday, so that is what's going to have to be done," Kerr said. "I think at least 14 or 15 under will probably win."
Michelle Wie was tied for 11th at 5 under after a 70.
Defending champion Suzann Pettersen was 2-under after a 71. Last year, the Norwegian star Pettersen overcame a nine-stroke deficit in the final round and won in a playoff.
It was nearly 30 degrees cooler Saturday following Friday's scorching 100-degree day. Players said lower temperatures made the 6,611-yard course play longer.
Miyazato birdied two of her final
"I had so much good today," Miyazato said. "My second shot was very well. But I had so much frustration on the putting on the front nine."
The Miyazato name is familiar on the LPGA Tour, though not Mika, but Ai Miyazato, winner of the 2010 Safeway Classic. Ai Miyazato, four years older than Mika, has nine career LPGA Tour victories.
The Miyazatos aren't related.
"Everybody asks me, "Oh, are you Ai's sister?'" Mika Miyazato said. "It's OK. I think everybody knows Ai, so I don't know if somebody knows me. I think it's lucky. Same last name, just different first name."
Ryu, the LPGA rookie points leader, briefly took the lead after shooting a 5-under 30 on
Kerr had birdies the three-hole stretch of par 5s from No. 8-10 to edge into contention.
"It gives me some good momentum going into tomorrow," Kerr said.
Michaels, an LPGA Tour rookie from UCLA, made an eagle at the par-5 ninth to pull within one stroke of the lead. She struggled late, hitting her tee shots into the water at 17 and 18.