Kazuhiro Yamashita and Shigeru Nonaka share a one-shot lead at the Japan Open after matching four-under-par opening rounds.

Yamashita dropped just one stroke during his 68, while Nonaka carded six birdies against two bogeys to claim a slender lead over seven players tied for third at three under.

Michio Matsumura, Han Lee, Toyokazu Hioki, Hiroyuki Fujita, Ryutaro Nagano, Taichi Teshima and Yuji Igarashi are all well placed just a shot off the pace.

Teen sensation Ryo Ishikawa is in a group tied for 10th at two under alongside Azuma Yano, Sushi Ishigaki, amateur Hideki Matsuyama, Katsumasa Miyamoto, Kenichi Kuboya and Naoya Takemoto.

Fresh from winning three of his five matches for the International team in the Presidents Cup last week, 18-year-old Tour money leader Ishikawa is firmly in the hunt for a fifth Japan Tour title of the season despite shipping three bogeys against five birdies during his first round on the Toyooka Course.

Katayama clinched his 25th career victory at last year's tournament to earn lifetime exemption on the Japan Tour.

Shingo Katayama made a solid start to his title defence with a level par 72, while last week's Canon Open champion Yuta Ikeda struggled to a two over 74.