Nasa Hataoka and Tokyo Olympics silver medalist Mone Inami were among a glut of home players making an early charge as the LPGA Japan Classic teed off on Thursday.
Hataoka, a six-time winner on the LPGA Tour, hit nine birdies and one bogey to card an eight-under-par 64 at the Taiheiyo Club's Minori Course, around 100 kilometres (62 miles) northeast of Tokyo.
Inami – who beat New Zealand's Lydia Ko in a playoff to finish second behind American Nelly Korda at the Tokyo Games two years ago – also hit 64 to join Hataoka and Yuna Nishimura one stroke behind leader Akie Iwai.
Ten of the world's top 30 players are competing as the LPGA finishes its Asian swing with a tournament co-sanctioned with Japan's JLPGA.
South Korea's world No 7 Kim Hyo-joo, the highest-ranked player in the competition, shot a 72 to finish the first round even par.
China's world number 12 Lin Xiyu fared better, carding a 66 to sit three strokes off the lead on six under.
Defending champion Gemma Dryburgh of Scotland was one stroke further back after birdying two of the last three holes.
Japan's Ayaka Furue, the 2021 champion, was also on five under, along with Korea's Jenny Shin and Switzerland's Albane Valenzuela.
South Korea's Jiyai Shin and American Rose Zhang, a winner on the tour this season, were on four under, while Australia's Hannah Green was on two under.