Cahill clinched his team's progression with two headers, the second coming in extra time after Syria took a shock lead on six minutes.

It brings his goal tally for the Green and Gold to 50.

Postecoglou, whose team has flirted with disaster throughout the campaign, was the most relieved man at ANZ Stadium.

A freekick by Syria, which blasted off the upright with seconds on the clock, was just centimetres from ending Australia's World Cup dream.

"Yeah we always find a difficult way to do things that’s been fairly consistent throughout qualification," Postecoglou told Fox Sports post match. 

"It’s a fantastic effort from the players physically. Timmy was Timmy and that’s why he’s our greatest ever."

Legend: Cahill keeps World Cup dream alive

Socceroos v Syria pic special

The Socceroos boss has come under heavy criticism for his team selections and formations over the course of the campaign, and threw up another surprise by benching Huddersfield midfielder Aaron Mooy.

But like he has done so many times in the past, Cahill ensured the Socceroos didn't leave empty-handed. They now face a playoff with CONCACAF's fourth-placed team.

"When (Cahill) broke the 100 games I said he’s a great Australian sportsperson and he’s got an international record that will stack up against the best in the world," Postecoglou said. "I can’t think of the last time he played 90 minutes and he’s played 120.

"These games throw up a lot of pressure and your looking for people who’ve done it before and can do what it takes."

"I told them just to keep going, we’re creating chances, we know we finish strong because the opposition have to stop us. They didn’t waver, or get frustrated.

"That’s what football's about, there’s a big prize at stake. Nights like tonight are where you build belief. We shot ourselves in the foot conceding a stupid goal but they kept going."

Brad Smith went down with an injury early in the match and Mooy was brought on. But there was no second-guessing by the coach about his original selection.

"It’s the nature of this qualifying process, we’ve done things differently the whole time but that’s not a bad thing, I’ve got full faith in these guys they keep trying and keep believing.

"I’m always comfortable (with my selections).

"It's disappointing for Smith to go down but those decisions I make with guys like Aaron, the physical toll of these games, he and (Tom) Rogic are our special players so we’ve got to be careful how we use them."