Veteran striker Tim Cahill scored deep into extra time to take Australia a big step closer to next year's World Cup and end war-torn Syria's fairytale run in the play-offs on Tuesday.

Cahill, 37, cancelled out Omar al-Soma's opener in the first half before he leapt to head his and Australia's precious second goal in the 109th minute for a 2-1 win in the second leg.

After last week's 1-1 draw in Malaysia, Australia won 3-2 on aggregate to reach a final play-off against the fourth-placed team from the CONCACAF federation, currently Panama.

Syria have never reached the World Cup and their hopes suffered a massive blow when Mahmoud al-Mawas was sent off for a second bookable offence in the fourth minute of extra time.

As penalties loomed, Robbie Kruse sent over a cross from the byline and Cahill powered his header past the diving Ibrahim Alma for his record-extending 50th Socceroos goal.

There was huge drama in the dying seconds, when al-Soma juddered the right post with a vicious free kick. But Australia survived to stay on track for their fourth straight World Cup.

"It was a fantastic effort from the players, they kept going till the end," said Australia coach Ange Postecoglou.

"Timmy was Timmy, that's why he's the greatest Australian player ever."

Syria, playing their home games in Malaysia because of the civil war in their country, had defied huge odds to finish third in their group behind Iran and South Korea.

But their inspiring run came to a shuddering halt against Australia, who were looking to recapture past glories at the same ground where they qualified for the 2006 World Cup, and also lifted the 2015 Asian Cup.

"What we have achieved with this national team is a great thing... our players were men on the pitch," said Syria coach Ayman al-Hakim.

- Go-to man -

Syria gave the home supporters some early palpitations. They opened the scoring after just six minutes when Mark Milligan gave away possession in midfield.

Tamer Haj Mohamad swooped onto the loose pass and fed the deadly al-Soma, who produced a superb finish to beat the approaching Australian goalkeeper Mathew Ryan.

Cahill may be in the twilight of his career but he showed that he remains Australia's go-to man in moments of crisis when he equalised just seven minutes later.

The Melbourne City man nodded Mathew Leckie's perfectly weighted cross into the back of the net for his 49th international goal, almost twice as many as his closest countryman.

The Socceroos dominated possession and always looked the more likely to score but were unable to capitalise on their chances, with the Syrian goalkeeper Alma proving a formidable obstacle.

Forced to defend for large periods of time, Syria created some dangerous opportunities on the counter-attack. But neither side could break the deadlock within the regulation 90 minutes, sending the match into extra time.

Syria quickly lost al-Mawas and Australia finally made their advantage count when Cahill climbed above the tired defenders to head home Kruse's cross, just 11 minutes from penalties.

There was huge drama in the dying seconds, when Soma hit the right post with a vicious free kick. Australia survived to stay on track for their fourth straight World Cup.

"It's amazing," said Cahill. "More than anything, it's my passion and in the end you get the rewards."