The round-of-32 clash with Egypt at Dallas Stadium on Friday (4am Saturday AEST) is the first time Australia's fate could come down to extra time and even penalties.
Some players could last more than 120 minutes, but others like exuberant young attackers Nestory Irankunda and Cristian Volpato likely don't have the tank.
It means Popovic must decide whether to start the youngsters or use them off the bench to finish the game off.
"That's always been the challenge when you have a young group that doesn't have the maturity or the experience of playing big games regularly," Popovic said.
"That's also the exciting part, the exuberance that they bring, the fearlessness that they bring.
"So we're managing all of that, and we have a wonderful group that is together, is united, and they're all playing their part.
"I'm confident we can see that again tomorrow, regardless of who plays and the players that come on and make an impact.
"We know how big this game is, and I think all the players are ready to deliver."
Popovic said the Socceroos were prepared for the prospect of penalties.
"We'd all prefer to win the game in 90 minutes," he said.
"But we've seen in the knockout games so far, they've gone to extra-time, we've seen a couple go to penalty shootout, one finish right at the end of extra time.
"So we have to be aware and prepared for all scenarios, and I'm sure the players will be tomorrow."
Popovic stressed on multiple occasions the Socceroos deserved to be in this position.
"You can never take being here for granted and never take any result for granted here at the World Cup," he said.
"And we deserve to be there. We've earned it. Fantastic football team, we are.
"Tomorrow's another chance to show each other our growth."
While the Socceroos squad, which has featured starting line-ups with an average of 24.6 years looms as one for the future, Popovic believes in them now.
"We believe the future is bright, of course, and there are many young players that aren't here at this stage that will be in the future as well," he said.
"But I've maintained all along that we wanted to deliver now with this group. We believe that they're good enough to deliver now.
"We've shown that already by getting through the group, a very difficult group, and we've done that through the quality that these boys have.
"Tomorrow is another opportunity to not think about the future, but to think about now, the present."
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