The Wallabies, who scored 13 tries, took a while to find their rhythm against a committed and tenacious Japanese defence, leading by only 23-3 at half time.
The Australia blindside flanker Rocky Elsom scored his third try of the match in the opening minute of the second half to record the fastest hat-trick by a forward in the cup's history.
A steady stream of tries followed, with replacement fly half Berrick Barnes bagging a double on debut. Full back Chris Latham and replacement wing Drew Mitchell also scored two tries each.
Barnes’ second try carried the total number of points scored in RWC history past 10,000.
Japan kept fighting but could not turn the ball they had into points.
Their solitary score came from fly half Kosei Ono’s long-range penalty two minutes before half time.
Wallaby captain Stirling Mortlock converted seven tries and kicked two penalties, while Matt Giteau kicked three conversions.
RNS mp/gs
