Australia bowed out with a 1-1 draw against Chile on Sunday, having needed a two-goal win to reach the semi-finals. Chile advanced to play Portugal for a spot in the final, with Germany taking on Mexico in the other semi-final.
The 48th-ranked Socceroos were lambasted at home for their disjointed performance in a 2-0 loss to a second string Germany, but held African champions Cameroon to a 1-1 draw and dictated terms against fourth-ranked Chile for much of the match.
"We're obviously very disappointed," Postecoglou told Australian media after the Moscow stalemate.
"We wanted to continue in the tournament, we wanted to get out of this group. That's what we came here for and we haven't, so we're just disappointed at the moment.
"We want to measure ourselves against the very best and we have. But we're not quite there yet so we'll keep pushing forward and making sure we keep developing.
"The players will get massive belief out of that. (But) it's definitely a missed opportunity."
Australia now turn their attention to qualifying for a fourth successive World Cup and face Group B leaders Japan in a crunch away match in the penultimate round in August.
Australia are third in the group, level on 16 points with second-placed Saudi Arabia, one point behind Japan.
They then play lowly Thailand at home in the last qualifier in September.
Postecoglou has taken a lot of flak from home pundits for persisting with an attacking formation instead of exercising caution but he has stuck to his guns, insisting that the team needs to take risks to improve.
"At some point in time I'll get replaced by 'John the pragmatist' and you can all be happy and revel in it," he said.
"I'll stick true to what I've started to do in this job with the same intention. We'll play a certain style of football, take it to opposition teams and see where it takes us."
(Writing by Ian Ransom; Editing by John O'Brien)
