Australia claimed their ticket to Brazil but fans' nerves were kept jangling in a manner befitting of the Socceroos' often tortured World Cup history.

Only seven minutes were left on the clock when Josh Kennedy, a peripheral figure throughout this World Cup campaign, scored the decisive goal shortly after entering the fray.

It may not have had quite the same heart-pumping ferocity as that unforgettable night eight years ago when Australia snapped their World Cup drought at the expense of Uruguay, but the roar of joy, combined with a fair dose of relief as Kennedy's header nestled in the net, was almost as intense as in 2005.

"I'm proud of everybody. It's been a really hard campaign but we showed our mental strength," the Australia captain Lucas Neill said. "I'm sorry it wasn't pretty but we beat them. We've got to keep pushing ourselves. Let's look at the positives tonight - we're going to Brazil."

In many ways Kennedy is an unlikely hero, having not played for the Socceroos since November 2011. His impact was doubly poignant given he had entered in place of hometown hero Tim Cahill, who was clearly displeased at being substituted.

The equation for the Aussies as they kicked off the match was simple. Win and their trip to South America was sealed. Anything less and their fate was dependant on the outcome of Oman's visit to Jordan a few hours later.

The message Holger Osieck and his players had been telling anyone who would listen in the lead-up was one of a team focussed, and with steely determination. The effort was certainly apparent, but the fluency and creativity were largely absent for long periods.

Cahill and Robbie Kruse combined after just two minutes with the former denied by the Iraq goalkeeper Noor Sabri. It was a near miss, but not the start of a theme, as the home side had hoped it might be.

Momentarily, it looked that the early goal would come from the most unlikely of sources as Neill crossed for fellow central defender Sasa Ognenovski but his free header went over.

At the other end Mark Schwarzer didn't have a save to make in the opening half. A very different scenario from when he defended his goal the last time Australia played a decisive World Cup qualifier on home soil.

As the impasse continued Socceroo fans, even those with not particularly long memories, started to cast a thought to past heartbreaks.

If Australia did little with the ball, Iraq were meek in possession.

They changed after the break. The gesticulations of Iraq's Serbian coach Vladimir Petrovic in the opening stanza were clearly delivered to his charges at the interval.

Iraq started the second-half much as Australia did the first with Saif Salman forcing a sprawling save from Schwarzer.

Nevertheless, Australia largely dominated the contest without finding any cutting edge in the attacking third. Wide men Kruse and Tommy Oar lacked the drive that had been displayed over the past fortnight, while Cahill was shackled.

The introduction of the skilful Tom Rogic at the attacking point of Australia's midfield livened things after the hour mark and the home side started to increase their threat without ever suggesting that a goal was imminent.

Iranian referee Faghani Alireza was cast as the villain for the large majority of the 80,523 fans after blowing for a foul momentarily before a Kruse volley hit the back of the net. The crowd may have been incensed but, tellingly, there were few complaints from Australia.

The Socceroos though, and perhaps the referee, were to be saved by Kennedy's trademark header. The Nagoya Grampus striker will get all the headlines, but it was the man who played in the cross whose role was decisive.

Eight years ago Mark Bresciano scored a priceless winner against Uruguay. This time it was his assist that was the veteran's telling contribution and ensured Australia are World Cup bound for the third successive time.