Ishikawa began the final round tied in the lead with Koumei Oda but as Oda slipped to a final round 75 it was Ishikawa who would go on to produce a final round of 69 to win comfortably.
Ishikawa, who is currently ranked 206th in the world, was playing his first event in Japan this year after a season on the PGA Tour which saw him make it to the opening event of the FedEx Cup Playoffs but no further.
Former winner, Kurt Barnes, continued his liking for the Wattsu Golf Club layout when he finished as the leading Australian albeit in 23rd position.
Brendan Jones was 36th and Won Joon Lee 50th.
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