Elsom joins Doug Howlett as the tournament's top try-scorer
Australia (23) 91
Tries: Sharpe, Elsom 3, Ashley-Cooper, Latham 2, Barnes 2, Mitchell 2, Smith, Frier
Cons: Mortlock 7, Giteau 3
Pens: Mortlock 2
Japan (3) 3
Rocky Elsom claimed a hat-trick as Australia overpowered Japan to get their campaign off to a winning start.
Japan lacked nothing in bravery, but Australia's physical superiority told as tries from Elsom and Nathan Sharpe put them 23-3 up at the break.
Kosei Ono's penalty was the least that Japan's valiant effort deserved, but they were over-run in the second half.
Debutant Berrick Barnes was among the scorers as an exhausted Japan conceded 10 second-half tries.
It was no surprise that Australia were happy to go for the direct route early on, with the Wallaby pack enjoying a significant physical advantage over their counterparts.
Australia tried to assert their authority - they are some 16 places above Japan in the world rankings - from the off but some stout and committed defence kept them at bay.
Japan had clearly earned the respect of their opponents and Mortlock took no liberties when two kickable penalties came his side's way, slotting both for a 6-0 lead after 16 minutes.
Ono scored his side's only points in Lyon
The two-time World Cup winners finally got over the line two minutes later when Sharpe emerged with the ball after a draining rolling maul.
Elsom benefited from a clever pass from Stephen Larkham to cross for his first try on 24 minutes, and soon after he claimed a second down the left touchline following Chris Latham's scoring pass.
Japan were still competing gamely though and when Mortlock tugged Hirotoki Onozawa's jersey to concede the penalty, Ono stroked the ball through the posts to get his side on the scoreboard to the delight of the crowd.
Australia made the perfect start to the second half, scoring within a minute of kick-off as Elsom cut a lovely line off of Larkham.
It was one-way traffic for most of the half as Japan's physical exertions of the first half saw them begin to fall off tackles.
Adam Ashley-Cooper finished off a flowing backs move, Latham burrowed over from close range and Barnes scored seconds after making his Test debut off the bench.
Replacement Drew Mitchell scored with his first touch, before George Smith created a try for himself out of nothing.
Mitchell, Latham and Barnes all added their second tries of the afternoon, while Adam Frier scored with the last move of the game.
Australia: Chris Latham; Adam Ashley-Cooper, Stirling Mortlock (capt), Matt Giteau, Lote Tuqiri; Stephen Larkham, George Gregan; Matt Dunning, Stephen Moore, Al Baxter, Nathan Sharpe, Dan Vickerman, Rocky Elsom, George Smith, Wycliff Palu.
Replacements: Adam Freier, Guy Shepherdson, Hugh McMeniman, Stephen Hoiles, Berrick Barnes, Drew Mitchell, Mark Gerrard.
Japan: Tatsuya Kusumi, Tomoki Kitagawa, Koji Taira, Nataniela Oto, Hirotoki Onozawa, Kousei Ono, Yuki Yatomi; Masahito Yamamoto, Taku Inokuchi, Ryo Yamamura, Takanori Kumagae, Samurai Vatuvei, Yasunori Watanabe, Hajime Kiso, Takamichi Sasaki (capt).
Replacements: Yuji Matsubara, Tomokazu Soma, Hitoshi Ono, Hare Makiri, Tomoki Yoshida, Yuta Imamura, Kosuke Endo