Iniesta scored the winning goal when Spain beat the Netherlands 1-0 in the 2010 final and has been a key part of a team that had swept all before it in European and world soccer over the past six years.
Iker Casillas and midfielder Xavi, who is struggling with injury, are likely to miss out in what will be a melancholy occasion with nothing but pride at stake. "We'll try to make sure that everyone who has come to Brazil plays at least once," said coach Vicente del Bosque. "We won't forget it is Iniesta's 100th game. He'll play."
Del Bosque said Pepe Reina, with David de Gea injured, would start in goal in place of captain Casillas, who has made a number of errors and conceded seven goals in two defeats in Brazil.
Xavi, dropped for the defeat by Chile and preparing for a move to Qatar, is not expected to be fit to make a farewell World Cup appearance.
"I don't think one game more or one game less will have any impact on how his career is viewed," said Del Bosque, who insisted it was wrong to heap all the blame for Spain's early exit on the older players.
"Why does everyone attack the veterans now? It is not only the veterans who are to blame."
Del Bosque added that the result against the Australians would not influence whether he stays on as Spain coach.