They didn't, Andy.
When they scored the second goal the normal thing to do was to get back asap and play for the third.
Instead, they spend 2 and a half minutes celebrating the 2nd goal. WTF?
And then they give the Serbs all the initiative, while they waste time during throw ins and waiting for a counter.
The Serbs were in shock, the Aussies knew that they have to go all in and score a third and a fourth. Instead, they give the ball to the Serbs, they waste time and they defend with 9, waiting for counters, when there are only 10-15 minutes to go.
That was very stupid logic.