Cahill struck in the second half of extra time to break the deadlock and keep the Socceroos on the road to Russia 2018.

It was agonising to watch at times as the hopes of both teams balanced on a knife's edge -  Australia forced to come from behind after Syria stunned the home crowd with a goal on six minutes. Then, as he has done so many times in the past, Cahill dragged his team back into contention.

By the end of the night he had notched up his 50th goal for the Green and Gold, following two trademark headers (13', 109') delivered in front of a crowd of just over 42,000.

Post-match coach Ange Postecoglou said of the 37-year-old: "That's why he's our greatest ever."

Even so Syria, reduced to 10-men early in extra time, were just moments from ending Australia's World Cup hopes when they struck the woodwork with seconds on the clock.

The Socceroos now face off against CONCACAF fourth place finisher, with Panama looming as the likely rival for a berth at the global showpiece.

As expected it was a tense clash, befitting a nervy qualification campaign which saw Australia finish outside the automatic qualification spots.

Postecoglou, often criticised for tinkering, made four changes to the side that drew 1-1 with Syria in Malaysia last week, with Cahill, Tom Rogic, James Troisi and Brad Smith coming into the starting XI.

In a shock move Huddersfield's star midfielder Aaron Mooy was benched for the crunch match. The Socceroos boss opted for three attacking midfielders and one holding midfielder. Hertha BSC's Mat Leckie was returned to the right flank and looked dangerous further up the park.

Cahill in the hunt for an astonishing 4th World Cup appearance took the armband and led the line.

Australia had not been beaten in Sydney since 2008 but any thoughts of lucky omens quickly evaporated.

Tamer Haj Mohamad punished Mark Milligan for a giveaway, launching a lightning raid and slipping the ball to Omar Al Soma on the left, the Syrian dangerman burying it into the high centre of the goal to the delight the more than 10,000 cheering Syrian fans.

Hearts were in mouths across the nation.

Moments later Smith was subbed with an injury to his left hip and Mooy was called into action. Then, just seven minutes after the visitors had stunned the Socceroos, Leckie fired in a clinical cross from the right and Cahill rose and headed back across goal for the equalizer.

The Socceroos were causing havoc down the left but the Eagles scrambled to keep them at bay. With the scores locked 1-1 (2-2 aggregate) at the break there were only two options for progression left to the home side: win the match outright or maintain the status quo and survive a penalty shootout.

Postecoglou's men continued to rack up the chances in the second-half  - a rocket by Rogic brought out a super left boot save by goalkeeper Ibrahim Almehbut with just 20 minutes to go.

It was a white knuckle ride and, for the fans of both sides, the tension was building with each passing minute.

At the end of regulation time, and almost 80 minutes after Cahill had bundled over the equalizer, the teams headed into extra time. The travel weary Syrians looked spent as they eyed another 30 minutes of combat. And it was about to get worse when Mahmoud Al Mawas was sent packing for a second yellow.

Boos rang out among the home crowd as a number of Syria's players hit the deck in what was seen as blatant time-wasting, and Socceroo supporters took to social media to vent.

Meanwhile sub Nikita Rukavytsya had two excellent chances on goal (not to mention a  penalty shout)  but Syria's custodian again proved Australia's nemesis.

With the minutes slipping away Cahill's moment had come, again, and the Socceroos' go-to man - the hero of the World Cup 2006 - latched onto a pinpoint cross from Robbie Kruse and headed the ball inside the top left corner to give Australia the win.

 

OUT: In a significant blow for the Socceroos Millgan and Leckie are expected to miss the intercontinental playoff due to an accumulation of yellows.