Miki Saiki shot a 5-under 67 to establish a one-shot lead over Sakura Yokomine after the first round of the Itoen Ladies on Friday.
Looking to build on her fourth-place finish at last week's Mizuno Classic, Saiki overcame a shaky start to knock in nine birdies against four bogeys at Great Island Club.
The Japan Women's Open runnerup is looking for her first victory since capturing her maiden title at the 2007 Fujisankei Ladies Classic.
Yokomine, second on the JLPGA money list, had a 68 that included six birdies and two bogeys, while South Korean trio Park In Bee, Kim Na Ri and Lee Na Ri all had 70s.