Both finished the 54-hole tourney at 14-under 200 after Yanagisawa, a former teammate of Tiger Woods at Stanford, carded a final round of 69 and Hiratsuka fired a 64.
Don Berry, Chad Saladin and Japan's Tatsuya Tanioka tied for third place at 11-under 203 at the Pearl Country Club.
Nobuo Serizawa was all alone in sixth place another two strokes back.
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