Brazil coach Carlos Alberto Parreira, while showing respect for his opposite number Guus Hiddink, is wary of what he sees as Australia's bruising style and has told his players not to get into a fight.
The two teams have three points after beating Croatia and Japan respectively in their opening games.
Australia's 3-1 victory over Japan was their first at a World Cup finals.
The Socceroos may rest four players who received yellow cards, Tim Cahill, John Aloisi, Craig Moore and Vince Grella, to make sure they are available for the final group match against Croatia.
Brazil set a record of eight successive wins at the World Cup finals by beating Croatia 1-0 on Tuesday.
"Australia are a very physical team but we are not going to fight with them," Parreira told reporters. "Our business is to play football, put the ball on the ground and impose our style and technique.
"It's a decisive match because whoever wins will almost certainly qualify."
Parreira also knows he is up against one of the world's canniest coaches in Hiddink, who led his native Netherlands to the semi-finals in 1998 and South Korea to the same stage four years later.
"He's a wonderful coach, one of the best in the world, and I have great respect for him," said Parreira.
The usually self-confident Australians have adopted a more cautious tone as they prepare to take on the world champions.
NO PRESSURE
"There's no pressure on us because everyone expects Brazil to win but there's also the fear that they probably haven't warmed up yet," said defender Lucas Neill.
"They are a team that can easily start to cook and we just have to make sure we don't let them boil against us."
Surprisingly, Australia won their last meeting 1-0 in the third-place playoff at the Confederations Cup in Japan in 2001.
Brazil coach Emerson Leao was fired as a result, learning of his fate as he was about to board his flight home.
The match will be a test for Ronaldo, top scorer at the 2002 World Cup with eight goals.
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Parreira has confirmed Ronaldo will start against Australia and says he is prepared to gamble on the Real Madrid striker.
But critics are wondering how long the coach's patience will last.
Brazil: (4-4-2)
1-Dida; 2-Cafu, 3-Lucio, 4-Juan, 6-Roberto Carlos; 5-Emerson, 11-Ze Roberto, 8-Kaka, 10-Ronaldinho; 9-Ronaldo, 7-Adriano
Australia: (4-5-1)
1-Mark Schwarzer; 7-Brett Emerton, 2-Lucas Neill, 6-Tony Popovic, 14-Scott Chipperfield; 8-Josip Skoko, 5-Jason Culina, 20-Luke Wilkshire, 23-Marco Bresciano, 10-Harry Kewell; 9-Mark Viduka
Referee: TBA
(additional reporting by Julian Linden)
