Schwarzer, one of the world's best goalkeepers and the Socceroos' most experienced player, appeared to struggle to judge the flight of the ball at corners at times during the win over Denmark while he also misjudged a backpass in the first half which almost gave the Danes a rare sight on goal.

The altitude in South Africa meant the ball flew around everywhere during the clash against Denmark, which was played at 1700 metres above sea level on the outskirts of Johannesburg, although Australia's first World Cup match will be played at sea level in Durban against Germany on June 13.

Schwarzer told Fox Sports after the win over Denmark that the balls being used would take some time to get used to for goalkeepers in particular at the world's biggest sporting event.

"Obviously it's quite unpredictable the way the ball flies," he said.

"Sometimes the ball has a genuine flight and other times it has a mind of its own so it has taken time to adjust and it will take us time still now (to keep adjusting).

"We have got to use this time between now and the first game on the 13th, where we are playing at sea level, to hopefully get used to the flight of the ball a little bit better and make things easier for ourselves.

"But the one thing you can't do is get frustrated because that is one thing that can happen to very quickly (as a goalkeeper) if you are not holding the ball like you would normally would if you are coming out for a cross and misjudging it.

"You have to stay calm and probably hold your run a bit longer and then go a bit later but it can be difficult because sometimes the ball (comes in) very, very quick as well."

Despite the problems dealing with the ball, the Socceroos still kept their 13th clean sheet in their past 19 matches in a good sign ahead of their three tough group matches against Germany, Ghana and Serbia.

"Our priority (against Denmark) was to make sure we defended well and we were organised and we limited them to only a couple of chances," Schwarzer said.

"So we are happy with the result and we know we can perform even better but the positive in the second half was we tended to finish the game quite strongly and that is positive knowing the (fitness) work we are doing (in training) is working well for us."