Both sides hopes of progression to the last 16 have been ended by successive defeats to Chile and the Netherlands, but whilst Spain have endured a nightmare defence of their title in Brazil, Australia have taken huge encouragement from their performances.
Ange Postecoglou's men had led the Dutch in the second-half in their last outing thanks to a wonder strike from Cahill and Mile Jedinak's penalty before being eventually losing 3-2.
"We've got one more game to go and it is not about Tim Cahill," said the New York Red Bulls forward.
"This last game is massive. If we beat Spain that will be one of the biggest moments in Australian history."
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Australia had arrived in Brazil as the lowest ranked side in the tournament, but far from being intimated by their more illustrious opponents they impressively took the game to Chile and the Netherlands in their two outings so far.
"It's going to be up to us again to go out there and get something out of the Spanish, and try to force our game on them," he said. "We've done that in both of those games and although we haven't come away with anything it's time we make that right.