Goals from James Troisi and skipper Mile Jedinak put the visitors 2-1 up in Kaiserslautern, following Marco Reus' opener, before a late Lukas Podolski strike salvaged a draw.
The result was the only disappointment for Postecoglou, having watching his side mix it with the world's best.
"I'm super proud. We threw some big challenges to some of our boys today and they were up to it," he told Fox Sports.
"I'm a bit disappointed we didn't get the win in the end... [but] now we push on.
"There's no limits. The Asian Cup was the beginning of something and tonight was another indication we're heading in a good direction.
"I would have liked to have won and I'm a bit disappointed we didn't do that but the other thing was the performance. It wasn't backs-to-the-wall.
"Yeah we had to defend strongly in the second half but besides that we matched them, we went toe-to-toe with the best in the world and that's what I'm most proud of."
Postecoglou was without the likes of Tim Cahill, Matthew Spiranovic, Massimo Luongo, Robbie Kruse and Trent Sainsbury due to injury.
The quintet were all key to Australia's Asian Cup success with Luke DeVere handed a debut in defence alongside Nathan Burns, Troisi and Mathew Leckie.
"I hope [this result] sheds us of any inferiority complex we might have of ourselves," Postecoglou added.
"I always said we believe our players are as good as anyone. This gives us a good foundation to keep moving forward.
"To see Luke DeVere play 90 minutes against the world champions, he's not anywhere near 100 per cent, but you see even right at the end he put [Podolski] off in that on-on-one.
"That's the belief Australian players have."
