Mizuno, 18, lies in a share of fifth on a two-round total of 147 (seven-over-par) and trails Britain's Alastair Hall by three shots. Hall, who opened with a fine 68, could only manage a 76 on day two but maintains a two-stroke advantage at the top of the leader board.
Japan's Takaya Tsuruta, Liu Yu Jui of Chinese Taipei and Fiji's Vikrant Chandra are tied for second on 144. Hong Kong's Terrence Ng finds himself six back on 150.
This week's winner will earn a coveted berth into next month's UBS Hong Kong Open.
144 Alastair Hall (UK) 68 76
146 Takaya Tsuruta (Japan) 75 71
Liu Yu Jui (Chinese Taipei) 73 73
Vikrant Chandra (Fiji) 71 75
147 Shinichi Mizuno (Hong Kong) 73 74
Huang Yen Ping (Chinese Taipei) 74 73
148 Olaf Allen (Fiji) 78 70
Edward Richardson (UK) 73 75
149 Chung Chen En (Chinese Taipei) 72 77
150 Terrence Ng (Hong Kong) 74 76