The Socceroos must beat Serbia to have any chance of reaching the knockout stages of the World Cup for the second time in a row but then they also have to rely on a favourable result in the Ghana-Germany game, which will also be played on Wednesday night (South African time).

The best case scenario is for Ghana to beat Germany, in which case Australia only has to beat Serbia to then make it through to the round of 16 while if Germany wins then Australia also has to make up a total of five goals on Ghana to get ahead of the Black Stars on goal difference.

The worst case scenario is if the Ghana-Germany game is a draw, in which case Australia would then have to beat Serbia - which has conceded just one goal in its two matches so far - by seven goals to qualify.

However Neill is hoping the Aussie fans will prove to be the team's '12th man' in Nelspruit.

While Australia has one of the largest set of travelling fans at this World Cup, unfortunately in its first two matches it also came up against two teams with plenty of support here in South Africa.

In Durban against Germany, during the 4-0 defeat, the Aussie fans only made up about 40 percent of the stadium while during the 1-1 draw against Ghana in Rustenburg the 'green and gold army' provided about 60 percent of the crowd.

But it is expected to be a different story in Nelspruit, given Serbia has one of the smallest set of travelling fans at this World Cup, with the Socceroos expecting the match to be virtually like a home game in Australia.

Neill said the support of the thousands of Australian fans in South Africa had been sensational so far as he urged the green and gold hordes to do everything possible to lift the team to victory in Nelspruit.

"In Durban we didn't give them anything to cheer about but they were huge for us (against Ghana in Rustenburg)," he said.

"The national anthem (before the Ghana game) was unbelievable and I was choking as an Australian (to hear the Aussie crowd signing) how could you be any prouder?

"There was a sea of Australian gold in the crowd and we were pleased to be able to put on a much better show for them (compared to the Germany game in Durban)."

And while the Socceroos know other results now have to fall their way in order to make the last 16, Neill said the least the Australian team owed the fans in Nelspruit was a win over Serbia - regardless of the result of the Ghana-Germany game.

"That is all people ask for when they come to the games - to see the players trying and we had that in abundance (against Ghana) and that is what we also have to do against Serbia."