Ask any Socceroos fan about their biggest worry for Thursday's match against Japan and most will say Ange Postecoglou's preferred three-man defence.
The 3-4-3 formation was first introduced in the 1-1 draw against Iraq in March and including that match, Australia has only won two of their past seven games - with some of the fixtures against world class opposition like Germany, Brazil and Chile.
A concern is how easily the back three has been carved up at times, particularly in the 4-0 friendly defeat against the Selecao and the 3-2 win versus Saudi Arabia.
But Postecoglou is a proud man and once he made the decision to change the formation, he was always going to live by the sword, die by the sword when it came to World Cup qualification.
It was always going to take time for the team to adjust and there were hugely positive signs with the structure in Australia's last match at the Confederations Cup - a 1-1 draw with Chile.
Despite the Chileans possessing world class players such as Arsenal's Alexis Sanchez and Bayern Munich's Arturo Vidal, the Socceroos were arguably the better team over 90 minutes, particularly in the second half.
The midfield press featuring Jackson Irvine, Massimo Luongo and Tim Cahill playing in an unorthodox right-sided position shackled the quality of the South American champions and didn't allow them time to play on the ball.
Mark Milligan quelled the threat of Sanchez in a defensive role and intriguingly none of Aaron Mooy, Tom Rogic or Mathew Leckie started the match - with only the latter appearing as a substitute.
The team looked dangerous in attack and created many chances, particularly in the second period, with only the finishing and final ball letting them down.
This was easily Australia's best game in their new setup and is the blueprint for how the team should perform moving forward with this formation.
Japan, like Chile, are a good technical side featuring quick and creative players like Borussia Dortmund's Shinji Kagawa, Pachuca's Keisuke Honda and Leicester City's Shinji Okazaki.
If the Socceroos team can function against Japan like they did against Chile, getting a win or draw in Saitama is a real possibility.
The questions are whether Milligan should be deployed as a centre-half again and if both Mooy and Rogic will be selected to start?
It may seem utterly insane to not pick your best two players, but there is no question the team performed better without both against Chile.
Don't be surprised if Postecoglou picks only one of Mooy or Rogic to start and tries to replicate the functionality of the team in their last match.
Milligan is a valuable asset driving the team on in midfield but the effect he had on limiting Sanchez in a defensive role cannot be understated.
Japan's Southampton defender Maya Yoshida was asked about Australia's biggest weakness and he immediately mentioned the formation switch.
"They’ve changed the shape a little bit – they have three at the back now," Yoshida said.
"I think they have a very good structure – strong and tall – but maybe [tactical] ability is their problem.
"Especially how I saw them concede the goal in the Confederations Cup. They had a guy running in behind them and they couldn’t manage it. That’s the point for us, I think, how many chances can we create like that?"
When the final whistle blows in Saitama on Thursday night, we'll certainly know a lot more about Postecoglou's formation and the nation's prospects in a potential fourth straight World Cup appearance.