The man widely regarded as the country's best player was sensationally left out of the starting team for the Socceroos' most important game of this qualifying series, the second-leg tie against Syria in Sydney.

As part of a tactical gamble that came close to failing spectacularly, Postecoglou cut Mooy from his lineup as part of a plan to be "more aggressive". It was followed by an unusual formation never used by Australia and uncommon at international level.

Australia came away with a dramatic 2-1 win in extra time.

Sources suggest the conversation heard at the training ground was as brief as Postecoglou saying: "You're not starting". When asked whether he was given any reason for being dropped, Mooy said: "Not really".

It was a shock to Mooy who was Australia's best performer in the first leg in Malaysia and, while he was coy on the subject, he admitted he was upset.

"Of course I was angry I wasn't playing," he said. "Every player should be angry that they're not playing."

The decision to cut Mooy backfired after just six minutes when Postecoglou's controversial system - a 3-1-5-1 formation which included three central attacking midfielders and just one holding midfielder - was left exposed by a Syrian counter-attack that lead to the opening goal for Omar Al-Soma. Australia gifted possession in an area of the field Mooy would have occupied.

"The formation was a bit different today. We hadn't played it before, we had three number 10s and one sitter [holding midfielder]. I came on in the number 10 position," Mooy said. "I haven't seen it [a system with three number 10s] either but it's the boss' ideas and we all believe it and go with it."

Mooy watched the opening goal from the sidelines, bracing himself for a long night largely spent as a spectator. However, he was given a chance to stamp his authority on the match after 10 minutes when an injury to Brad Smith required a substitute.

Mooy showed why he deserves a starting place with another impressive performance. He played a role in setting up Australia's two goals that sealed their 2-1 extra-time victory over Syria.

Despite playing with three number 10s - Mooy's preferred position - Postecoglou dropped the Premier League regular in favour of Melbourne Victory's James Troisi in order to be more aggressive. The initial plan was to use Mooy as an impact player later in the game and had it not been for an injury to Smith so early in the match, Mooy could have languished on the bench until the second half.

"It's just a decision on selection. We wanted to be a little bit more aggressive in attack and, um, Aaron was the one to miss out," Postecoglou said. "It's not the first time he's missed out and it won't be the last time he misses out. Unfortunately Smithy struggled with his injury and unfortunately we had to make a change.

"I thought Aaron made a difference, I thought Tomi Juric made a difference when he came on and I thought Nikita [Rukavytsya] grew into the game and also made an impact which was going to be important tonight," Postecoglou said.

"We kind of knew in the back of our minds that it could always go into 120 minutes and if it did we needed people coming off the bench to make an impact."