PHOENIX, Arizona, March 14, 2013 (AFP) - Miyazato, who finished second in this event last year, leads South Korea's Jee Young Lee, who equalled the previous course record at Wildfire Golf Club with a seven-under 65.
"I hit the ball well and my putting was really good," said Miyazato of bogey-free round. "I think I had good course management as well and I could control myself really well, too, so it was a good day."
Thailand's Pornanong Phatlum, Taiwan's Candie Kung, and Americans Gerina Piller and Brittany Lang share third place after they shot rounds of 66.
Australian Katherine Hull-Kirk, Sandra Gal, Jiyai Shin and Lexi Thompson are one shot adrift in seventh at 67.
"You know, it's just beautiful out there," Miyazato said. "It's just always nice to play in this tournament, it's very enjoyable, and I just had a good feeling this morning."
Indeed as Miyazato began her round with a birdie at the opening hole followed by three-consecutive pars.
She made two more birdies at No. 5 and the eighth before making the turn at three-under.
Miyazato tacked on another birdie at the 11th as she was able to charge up the leaderboard by picking up five shots over a four-hole stretch.
Her hot streak included a birdie at No. 14, followed by an eagle at the par-five 15th.
She then posted back-to-back birdies at the 16th and 17th before closing with a par at the last.
Defending champ Yani Tseng posted a two-under 70 in her first round to take a share of 39th place.
Paula Creamer, who along with Miyazato suffered whiplash injuries in a car crash in Thailand, shot a three-under 69 and is tied for 21st.
Natalie Gulbis was forced to withdraw from the tournament on Wednesday after she was diagnosed with malaria.
The American pulled out of the tournament after first becoming ill while playing in a LPGA Tour event two weeks ago in Singapore.
Leading first round scores on Thursday at the LPGA Tour's Founders Cup (par 72, USA unless noted):
63 - Ai Miyazato (JPN)
65 - Jee Young Lee (KOR)
66 - Phatlum Pornanong (THA), Gerina Piller, Candie Kung (TPE), Brittany Lang
67 - Katherine Hull-Kirk (AUS), Sandra Gal (GER), Jiyai Shin (KOR), Lexi Thompson
68 - Jennifer Gleason, Danielle Kang, Amy Yang, Angela Stanford, Stacy Lewis, Lindsey Wright (AUS), Jimin Kang (KOR), Juli Inkster, Eun-Hee Ji (KOR), Kris Tamulis