This is it for Ange Postecoglou.

Tonight marks an unfamiliar fork in the road for the Socceroos coach that, in many ways, will shape the legacy he leaves when he departs at the end of this World Cup cycle.

Get through tonight, and Australia's mission to qualify for a fourth straight showpiece continues next month, with Panama or Honduras the probable antagonists.

Fail, and the 52-year-old's tenure will be capped at 1,448 days.

Whichever path tonight's second leg against Syria takes, he insists his future is not at the forefront of his mind.

"There's always that possibility every game, that I could be gone," Postecoglou said.

"I don't think that way, mate. That kind of stuff doesn't really enter my thinking.

Postecoglou has seen Australia reach some of its highest points, but missing out on Russia 2018 would be a big failure. ( AAP: Julian Smith )

"I've coached my country now for 11 years … more than I have club football.

"I've never taken it for granted and I certainly don't think about myself in this situation, whether it's the first or last game.

"I've been pretty big on preaching to the players to treat every one like it is your last and that way you appreciate every one of them.

"If Tuesday is it for me then I won't go into it with any different feeling than I have any other game.

"[But] I don't take it for granted that I'm coaching my country … every time we play it's a great honour, and when you play at home there's always a buzz."

Much has been achieved since Postecoglou's appointment on October 23, 2013.

The Socceroos' World Cup qualification hopes are on a knife's edge. ( Reuters: Lai Seng Sin )

After ushering out the veteran generation he inherited, the dual A-League title-winning mentor set about leading Australia to its historic 2015 Asian Cup triumph, an even grander feat given the national team's world number 97 ranking when the tournament kicked off.

But the honeymoon is long forgotten, and how smoothly the divorce proceedings pan out depends very much on whether the Australian public have a reason to turn on their TVs during the early hours next June.

Postecoglou has drawn stinging criticism for the Socceroos' current state of flux, his admirable — and equally stubborn — refusal to deviate from his expansive philosophy a key source of provocation.

Fuelling angst is the timing of, and inconsistencies since, installing his back-three formation in Tehran this March, a move that may have cost Australia direct qualification.

Yet pragmatism has never been Postecoglou's bag, and should his unapologetic vision steer the Socceroos to a strong Russia 2018 campaign with post-golden generation personnel, he may be saluted as one of the team's best-ever coaches.

By Postecoglou's own admission, failure to qualify from the group last month was far from ideal.

Honduras or Panama likely await Australia if it can navigate its way past Syria tonight. ( Reuters: Darren Staples )

If there's a silver lining, it's the battle-hardening nature of home-and-away play-offs.

"It's not a bad alternative [in the sense that] if we didn't have these games we'd just be having friendly games, and it would have been hard for us to get any major games," he said.

"We'll still get enormous games in this scenario out of the next three games.

"For this group of players, if they come through this then belief just grows … and that will hold us in good stead going forward."

AAP