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 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 beckoned, Robbie Kruse sent over a cross from the byline and Cahill out-jumped his marker to power a header past the diving Ibrahim Alma.

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