The showpiece kicked-off in controversy on Thursday after Japanese referee Yuichi Nishimura awarded a penalty that helped hosts Brazil start their campaign with a 3-1 win over Croatia in Sao Paulo.

Nishimura ruled that Fred was brought down in the box. However, replays showed there had been minimal contact.

In the wake of the controversy, there are suggestions referees may be gun shy when it comes to making similar decisions during the rest of the tournament.

Socceroos striker Tim Cahill said on Wednesday he expected there to be shirt-pulling and nudging by the Chileans in the box during their crucial first clash in Cuiaba on Saturday (AEST). But Postecoglou wouldn't get drawn into the matter.

"All the teams have had a visit from the officials and they've told every country what they're looking for, so we're aware of what they're looking at," he said.

"The referees have got their job, we've got ours so we won't sit there and try and pre-empt what may or may not happen. We've been told the things that are going to be highlighted at this World Cup and we'll deal with it accordingly."

While the Chileans may look to nullify Cahill's aerial advantage, Postecoglou said he wasn't Australia's only threat.

"We're working on a few things and we certainly believe we can be a threat in other areas," he said.

Postecoglou emphasised there were no concerns over Mark Bresciano's fitness and indicated the veteran midfielder would start.

● Meanwhile, FIFA have ordered the Socceroos to change their strip for their opening match.

They were due to wear the traditional gold shirt and green shorts but will now play in gold shorts after FIFA ruled the green would have clashed with Chile's blue shorts. AAP