Forwards Lukas Podolski and Miroslav Klose gave their side a 2-0 halftime lead to vindicate coach Joachim Loew's faith in them despite a recent lack of goals, with winger Thomas Mueller and substitute Cacau finding the net after the break.
Australia, who started both halves brightly and battled gamely throughout, played the last 34 minutes with 10 men after Tim Cahill was dismissed for a foul on Bastian Schweinsteiger.
Germany lead Group D from Ghana, who beat Serbia 1-0 in Sunday's earlier match in Pretoria.
It was the triumvirate of captain Philipp Lahm, Mesut Ozil and Mueller who laid the foundation for victory as the young German team took to the wings to outflank the much-vaunted Socceroo defense.
In the eighth minute, Ozil found Mueller in what looked to be an offside position and his cutback allowed Podolski to sweep the ball into the net via Mark Schwarzer's flailing arm.
Klose should have doubled the lead in the 24th minute when he blasted wide when Podolski's cross left him free in front of goal but he made amends just two minutes later.
Lahm lofted a high cross in from the right, Schwarzer came charging out to claim the ball but Klose beat him to it and headed into an empty net for his 33rd international goal.
With the Australian spirit sapped by Cahill's sending off, Mueller got his reward for a fine performance on the right flank when he found space in the box and screwed the ball into the net off the post in the 68th minute.
Cacau, who had just replaced Klose, completed the scoring two minutes later after Ozil had beaten the offside trap to play in the Stuttgart striker.
