An enormous, loud, explosive bang, one which would send even more tremors through a football world which has already been shaken it to its foundations by events in Brazil.

Can Australia beat Spain, whom it meets in their last group fixture - now the deadest of dead rubbers - in Curitiba early next week?

Even two days ago the question would have seemed absurd. But, on the evidence of a week of World Cup football, it's not such a daft inquiry at all.

The Socceroos arguably, save for five minutes of madness against Chile in their opening game, could be going into this match with two draws under their belt and a real chance of qualifying if they could beat the dethroned world champions.

After all, Australia's results against the Netherlands (2-3) and Chile (1-3) are much better than the Spaniards' (1-5 and 0-2).

And it's not just the results although they, in the end, are all that matters.

Australia has performed with huge credit - its muscular approach allied to a structured commitment to passing and attacking has won fans all over the world -  but Spain's efforts, given the quality at its disposal and the records it has set, have been abject.

Spain, the masters of the universe these past six years, have not just been dethroned; its demise has been like one of those coups in which the ruler of a one-party state has been overthrown and he and his family taken out in the city square and summarily executed by gun-toting rebels.

For Spain had exerted its own version of a footballing tyranny, holding the world under their heel.

Victorious in the 2008 and 2012 European Championships and the 2010 World Cup, its dominance was greater than any other nation had achieved in the modern era.

Not only that, but its club sides ruled the roost in Europe: the Madrids of Athletico and Real contested the Champions League final less than a month ago, while Sevilla took out Europe's secondary Cup, the Europa League.

Barcelona had set a standard by which all had to be judged with its stupendous play for four or five years and it barely seemed as though anyone else would ever get a look in.

But eras end: sometimes slowly, with a painful decline as great powers wither into irrelevance, and sometimes dramatically and violently, in revolution.

This looks to be of the latter variety, and why shouldn't Australia fancy its chances of delivering the coup de grace?

Spain's tika-taka football, or at least the version it now performs, is a pale imitation of the style that once delivered death to its opponents.

Older, slower, less hungry and simply tired and worn out, this Spain looks vulnerable and ready for the taking.

Of course there is always the risk that a great champion has one last great effort still in his locker, and the possibility of enduring the sheer ignominy that would be occasioned by a loss to the footballing minnow of Australia might be enough to galvanise the Galacticos.

Which is why it would be folly to say Australia will beat Spain. But, on what we have seen so far, there is a chance that it might.

And that speaks volumes not just about the decline of the once-great champions, but of the progress the upstart Aussies have made in two games.

The rollercoaster game against the Netherlands was the best of what has been a marvellous tournament so far, a match in which unconsidered Australians showed it had what it takes to go toe-to-toe with a side many fancy to win the entire tournament.

It also performed with great credit against Chile aside from a horror period when, overawed and frozen in the environment, it conceded two goals.

It's no good rueing what might have been.

Coach Ange Postecoglou has insisted all along that this World Cup is not just a learning experience and he will be desperate to ensure Australia does not go home empty-handed.

It's up to him and his players to ensure this momentum continues. What better way to do so than by completing the interment of the fallen champions?

Postecoglou has promised that the Socceroos will take the game to the Spaniards, and why wouldn't they?

The ''attack is the best form of defence'' mentality has put them right in the two games they have already played against two of the World Cup's form teams.

The coach has always insisted that it is his team structure and tactical approach that is paramount, which will be put to the test in the Spain game as numerous first team players will be missing.

Tim Cahill, the talisman whose final World Cup game produced such a brilliant sign-off goal, will be missing through suspension.

Mark Bresciano's ageing body is unlikely to stand the rigours of another tough 90 minutes on such a short back-up.

Mark Milligan missed the Dutch game through a hamstring injury, and must be in doubt.

Ivan Franjic has already gone home, injured in the opener against Chile.

No matter.

Postecoglou put his faith in squad players Ryan McGowan and Matty McKay for the game against the Netherlands, and both did enough to retain their places.

If Bresciano can't play, then Oliver Bozanic impressed off the bench to suggest he should be given a chance from the start.

No Cahill? Well, the Socceroos are going to have to learn to live without him, so why not give Adam Taggart a go from the start.

And Ben Halloran, used off the bench in both games, might warrant a chance for the full 90.

Tommy Oar has not been as incisive as might have been hoped, so perhaps starting Halloran on the left, or switching the impressive Mathew Leckie to that side and playing Halloran on the right, could be an option.

The biggest question is the goalkeeper.

Mat Ryan came into this competition as Postecoglou's clear number one choice, but in truth he has had a World Cup to forget.

There was criticism in some quarters of his positioning against Chile, and he has to carry the can for the critical goal against the Netherlands, when his dive was too late and his wrist not powerful enough to deflect Memphis Depay's long-range drive.

Does Postecoglou drop the young goalkeeper to give Mitch Langerak or Eugene Galekovic a chance, or does he stick by his shot stopper and show that he has faith in him so as to bolster his confidence?

Ryan certainly can not afford any errors like the one against the Dutch, but those who know him say he has the mental strength to come back and be a better goalkeeper as a result of this learning experience.