Socceroos ready to go up a gear in high-stakes US clash

Australia stunned Turkey 2-0 with a brilliant performance where they were superb defensively then hit their more-favoured opponent on the counter.

But the US, who beat Paraguay 4-1 first up, pose a different test, regardless of whether star attacker Christian Pulisic plays.

"It's a different challenge. Different teams. Turkey were a more European style in terms of their technical build up, slower build-up, fantastic possession," Popovic said.

"I think the United States team has a good mix of the two: very powerful, very athletic, so we know it will be a different type of challenge. 

"Playing the host nation here as well is a wonderful challenge, but also a wonderful opportunity for us, and we know that we will need to be better than we were against Turkey to get the result we want."

Popovic shocked Australia when he dropped captain Maty Ryan and vice-captain Jackson Irvine for Patrick Beach and Paul Okon-Engstler respectively against Turkey, while also starting Nestory Irankunda.

All three big calls paid off in spades, though whether Popovic will back the same 11 again is unclear.

After fielding 10 World Cup debutants first up, Popovic expected them to be better for the experience.

"I think they'll go into the game understanding their roles better, being more comfortable out on the big stage, and I'm confident that these boys can have another level that they can go better again," he said.

"... If we can be present again tomorrow and play with that same confidence and belief, we can really put on a good show."

Socceroos defender Harry Souttar was wary of a fast-starting US, while their coach Mauricio Pochettino made it clear his charges need to match the intensity, mindset and belief of the Socceroos.

"It's difficult to play against a team that really believes in what they are doing," Pochettino said.

Popovic has relished watching the evolution and maturation of his group since last October's feisty 2-1 loss to the US in Denver - believing they are a better team now.

"It's been building, and that (Turkey win) was a game that it all came together in terms of the belief being present in the moment, understanding it's a World Cup for a lot of the boys for the first time, but playing as if they belong there," he said.

"And we'll need that again tomorrow, because it's a wonderful opportunity tomorrow for us."

Popovic said he had a full squad of 26, while the Socceroos are prepared for every scenario involving Pulisic, who Pochettino wouldn't rule in or out of the match as he battles a calf injury.

While much of the build-up has focused on US pundits writing off the Socceroos, there are bigger things at stake.

If Australia win, they could top group D with a game to spare.

Even a draw should seal progression, depending on how Turkey and Paraguay fare in their clash.

The group winners will play a best third-placed team from one of groups B, E, F, I or J and get to stay on the west coast, with their round-of-32 game in Santa Clara.

The runners-up hit the road to Arlington, Texas, to play the group G runners-up - either Belgium, Iran, New Zealand or Egypt.

For the best third-placed teams, things get more complicated, with tougher round-of-32 opponents.

But neither Popovic nor Souttar are thinking about permutations.

"First and foremost, we're not thinking ahead at all," Souttar said.

"It's literally just about the game tomorrow, and how we approach it, how we start the game."