The Dutch produced the performance of the tournament so far by thrashing defending champions Spain 5-1 on Friday.
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“I can’t see why we should worry more [after Netherlands' win], we have been preparing for it all this time," he said at Tuesday's pre-match press conference.
“We’ll have to be much stronger defensively, you saw what their attack did to Spain. But we are at risk if we just think about defending.
“There will be only one outcome if we just do that, so we will also have to do well on attack.
“Look at Spain. They would have had better luck if they had attacked better. And that’s what we should have in mind."
Postecoglou is aware of the attacking threat posed by Louis van Gaal's men - Arjen Robben, Robin van Persie and Wesley Sneijder all impressed against Spain - but the former Melbourne Victory boss accepts there is more to the Oranje than just their marquee trio.
“It will be hard to face the likes of Robben and Van Persie, we know that, but others also might step up if you leave them too much space. We’ll try to work on this in a collective manner," he added.
“It will be a great challenge, there’s a lot at stake for both sides. Netherlands can assure qualification, and it will be the end for us if we lose. So I’m expecting a high quality encounter.”
Defender Ivan Franjic is out of the World Cup with a pulled hamstring, with Ryan McGowan his likely replacement at right-back.