Defence coach John McFarland says the Springboks expect Japan to play a quick game in Brighton on Saturday.
While the Boks should kick off their World Cup campaign with a convincing win against a team ranked 13th in the world, McFarland talked up the Brave Blossoms on Monday.
'Japan definitely pose a threat with the speed of their game and it is up to us to control the pace of the game,' said McFarland. 'They've got some players with Super Rugby experience and they are a well-coached team, coached by a guy who has been involved in winning a World Cup [Eddie Jones].
'We are expecting a quick game and for them to try and take us off the pace of our game. So we must be ready for anything.
'We've watched nearly 20 games of theirs over the last two years and think we now know them inside out. They keep the ball well, they've got some good players.'
But he insisted the Springboks were more concerned with successfully executing their own game plan.
'It's about how we play but obviously there will be small tweaks we will make game by game. Samoa [who are also in Pool B] will certainly have some big blokes trucking it up the channels. So you make small adjustments in each game, but it is about how we play and what we do.'
McFarland added that the Boks' fitness had improved since the Rugby Championship, where they ran out of steam at Suncorp Stadium and Ellis Park.
'We've worked very hard and certainly all the testing has shown that the conditioning levels have increased dramatically and you can see it in our game stats over the last eight weeks. Guys were getting up off the floor quicker. But the test is always on game day and that never changes.
'If you are in good shape you get up quicker, you feel better, you are confident.'
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