It came in the form of 20-year-old rookie wingback Alex Gersbach, who fully vindicated Postecoglou's decision to hand him just his third cap.
Gersbach won the 60th minute penalty, which Milligan duly converted to earn Australia a 1-1 draw with Cameroon at St Petersburg Stadium.
And his energy, willingness to chance his arm and unabashed verve, were welcome additions to a team in need of a minor miracle going into their final Group B game against Chile in Moscow on Sunday night (Monday AEST).
Only in the squad because of injury to Brad Smith, Gersbach was Postecoglou's wildcard and he looked at ease on the big stage.
The performance earned praise from both coach and captain.
"Alex was excellent," Postecoglou said.
"He's got great technique. He's got great composure and did well for the penalty. He put a couple of balls in ... one in the first half went just over Tomi Juric's head that would have been a great goal.
"We've got some good young players coming through. These guys will be together for the next four to six years.
"We'll keep exposing them at this level."
Milligan was also impressed, saying the former Sydney FC defender's youthful fearlessness was an advantage.
"It's the beauty of being that young ... he's told to be nice and aggressive and and positive and he just goes and does it," Milligan said.
"I think he was on holidays a couple of weeks ago, considering everything he's come in and done a wonderful job today."
Echoing Milligan's thoughts defender Bailey Wright was also impressed with the Rosenborg flier's willingness to burst down the line and cross and also dart into the box, which drew the spot kick when he was upended by Ernest Mabouka.
"Alex did really well ... he came in late but he's in good shape and you saw today that great bit of play from him (for the penalty)," Wright said.
"He's really direct ... and both sides of the game was really good.
"Credit to him he is still a young lad and he looked really comfortable out there."
Gersbach is almost certain to start again on Sunday night as the Socceroos seek to find a way of beating Chile - a feat which looks beyond them on current form.
While many will see it as a bridge too far, Milligan insisted: "We won't be going in just hoping ... we will prepare now to go and win just as we always do.
"Chile a are very good side but they have weaknesses as well.
"If we continue to get better at executing what we want to do, then we will get there.
"Tonight we are a lot braver in the way we defended (as compared to the 3-2 loss against Germany).
"And that will be very important on Sunday against Chile."