France performed in fits and starts - a rusty display; they will have to lift significantly to threaten in the latter stages, though they often do exactly that. For most of the match, they tried to go too laterally before going forward. It meant Japan could cover well - and they showed they are developing into a reasonable international side; no longer cannon fodder.
For France there are early concerns. On this evidence Raphael Lakafia lacks the pure mongrel of Sebastian Chabal - the man he deposed - but may develop into something resembling him by the business end of the tournament. Their midfield defence was breached easily at times and will have to improve substantially in this area to withstand the attacking barrage to come later in the tournament.
Coach Marc Lievremont will be worried about the relative ease in which Japan were able to retain possession and the way replacement forward Alisi Tupuailai and flanker Michael Leitch caused chaos with their charges.
"There was a window to win the game," said Japan coach John Kirwan. "We talk about inches at this level and that is all it was. There was a couple of decisions that went against and one knock-on at a crucial time."
Kirwan had sensed a bit of panic in the French ranks, and knew they were there for the taking.
"They didn't know a lot about us and at halftime we knew they had got two tries off our turnovers. In the second half when we started to come back they looked concerned... You can't practise for World Cup pressure."
For his part, Lievremont said: "We were complacent after the first two tries - maybe we thought it was going to be an easy evening. Overall there are warning signs and it wasn't a great evening for us. The Japanese played very well and probably didn't deserve to be beaten by such a margin."
France should have scored twice in the first three minutes, before lock Julian Pierre crashed over in the fourth minute. When Francois Trinh-Duc snaffled an intercept to sprint 50 metres and score in the 11th minute, a rout beckoned. But Japan worked their way into the match. After a penalty goal, Arlidge scooted through for an opportunist try after half an hour to give them hope before French winger Clerc scored their third try three minutes later.
In the second half, Japan stretched France with their helter-skelter approach. Arlidge brought the house down with his second try in the 48th minute and a penalty reduced the deficit to four points. After further Japanese chances, Nallet's try finally made the game safe.
France 47 (J. Pierre, F. Trinh-Duc, V. Clerc, L. Nallet, P. Pape, M. Parra tries; D. Yachvili 4 cons, 3 pens) Japan 21 (J. Arlidge 2 tries, 3 pens, con). Halftime: 25-11.