A 5-1 win over Jordan in Sydney saw the Aussies top Group B with seven wins from eight games, ensuring a high seeding for the next stage which will see the 12 successful teams split into two groups, with the top two from each group automatically earning a ticket to Russia.
Coming on top of last year's Asian Cup triumph, the coach said it was time critics started to show some more faith in the national team.
"I mean, I don't get it. Just watch what the team's doing ... that should tell you enough, Postecoglou said.
"We're not going to be worried about who we get in our group. We've had some tough groups in every competition that we've been in.
"We had a tough group in the World Cup, we had Korea in our group in the Asian Cup.
"We've had Jordan - who, don't forget finished fifth in the last World Cup campaign in the play-off spot - in our group again.
"And we've overcome all those things.
"So whoever we get, we get, and we'll go at them."
Just which teams Australia will have to overcome to reach the World Cup finals for the fourth consecutive time will be revealed on April 12 when the draw is conducted in Kuala Lumpur.
As they were in last week's 7-0 win over Tajikistan in Adelaide, the Socceroos were dominant against Jordan, racing to a 3-0 lead by half-time after a double to Tim Cahill and a precision strike by Aaron Mooy.
Jordan, which beat Australia 2-0 in Amman in October, had no answers, manager Harry Redknapp lamenting the lack of professionalism within the game in Jordan.
"The whole structure of the set up needs work. There is so much work needs doing," he said.
"We had no analyst on the opposition, no sports scientist.
"The players all play in Jordan, most of them. They are short on fitness. So when they play better teams they struggle for fitness.
"What can you do?"
The only concern for the Socceroos was a horror tackle by Yousef Ahmed Mohammad on Robbie Kruse, who was playing his first game for the side since the Asian Cup final.
Kruse was outstanding with three goal assists before being cut down in the second half, with commentators and fans incredulous the offender didn't cop a red card.