The Everton player said Wednesday's game was the hardest they would face on the road to South Africa 2010, and they should take nothing for granted despite sitting top of Asian Zone Group 1.
"Qualification seems a long way away, really, so we cannot get ahead of ourselves," Cahill said. "We need to keep our feet firmly on the floor and really concentrate on putting in a good performance. Hopefully, we will get results."
"I feel that we have prepared well. We feel very excited," Cahill said after a brief training session, with several of his team-mates still on their way to Japan from clubs dotted around Europe.
The Australians will have the psychological edge over Japan after the Socceroos beat them 3-1 at the 2006 FIFA World Cup, with Cahill scoring twice late on.
"I think (Japan feel) they must win this game," McDonald said. "We feel that we must win as well. If we could do that, we will be one stop closer to the World Cup, and that's what we really want."