Luke Donald fired a 7-under 64 on Friday to take a 4-stroke lead after 36 holes of the Dunlop Phoenix.
Donald completed two rounds at 13-under-par 129 at Phoenix Country Club.
Shunsuke Sonoda posted a 66 to move into second place at minus-9, while Hiroyuki Fujita also had a 66 to finish two rounds in third place at 7-under- par 135.
Donald got off to a fast start with birdies on 10 and 11. He also converted birdie efforts at 13 and 15 to move to 10-under. The third-ranked player in the world carded three more birdies on the front nine to move four clear of the field.
Koichiro Kawano posted a 2-under 69 and is alone in fourth at 6-under 136. Last year's winner, Toshinori Muto, carded a 2-under 69 to move into a share of 11th at minus-3. Alvaro Quiros (69) is among the seven players tied with Muto.
Nicolas Colsaerts (71) and Ryo Ishikawa (67) are among six tied for 19th at minus-2.
Shigeki Maruyama, American Ricky Barnes and Italian Edoardo Molinari were among those that missed the cut.