Springboks openside flanker Heinrich Brussow and Australia's David Pocock are set to go head to head in a clash that should go some way towards deciding which country meets New Zealand or Argentina at the semi-final stage next weekend.
"The breakdown will probably be the defining factor of the game this weekend for both teams, on attack and defence," South Africa assistant coach Gold said. "The guys who master the breakdown the best and adhere to the referee's interpretations the best, are probably going to be in the best position to win this game.
"For those players it is such a fine line between being a genius or breaking the law."
South Africa are bidding to become the first back-to-back world champions following their success at England's expense in Paris four years ago.
And they are viewed as the team most likely to halt red-hot tournament favourites New Zealand in their tracks.
"To be honest, in the back of our minds it is something we would like to achieve, but it is not something that is spoken about on a daily basis," Gold added. "Sure, it's a motivation at the back of the minds to be successful, but it doesn't affect us too much.
"The players are quite calm at the moment. The training sessions have gone well this week and the enormity of the situation is certainly something we are aware of.
"Ever since we went into camp in Johannesburg, we spoke about the responsibility that all of us have got to everyone back home.
"We know the strength of the support back home and it is something that is very important to us."
Australia beat South Africa twice en-route to winning the Tri-Nations title earlier this year, and Gold has no doubt they will pose the Springboks a severe examination.
"I think the Australians were a very good team, obviously, in the Tri-Nations, and they haven't got any worse, let's put it that way," he said.
"The core of the team at the moment, having had so much success for such a long period of time, to slip up against a team as good as Ireland hasn't really affected them and they are still in the quarter-final.
"The Australian team can live, physically, with the best at the moment. They are a very young and athletic side and they have exciting backs that will move you around the park.
"And they have forwards that can keep up, so they are a dangerous team. "We've worked hard on them and we will give them the respect they deserve this weekend.
"But from our point of view we have our strengths as well, and it is important we concentrate on what our strengths are."
Australia coach Robbie Deans, meanwhile, has told his players their record against South Africa is meaningless at a World Cup.
The Wallabies have won five of the last six meetings between the Tri Nations rivals.
They also enter Sunday's quarter-final at Wellington Regional Stadium with three successive victories against the Springboks in the bank.
Deans, however, insists the World Cup is a different stage with different demands.
"All that matters is Sunday. The winner goes on, the loser goes home," he said.
"Taking comfort from previous games is the quickest path way to the airport.
"The knock out phases of the World Cup are completely different to every other type of rugby we play - the stakes are higher, the intensity greater and the margins between success and failure smaller.
"We've seen that to some extent already in the tournament through the key pool matches and you can pretty much guarantee that it will only intensify from here.
"History will be created this weekend and we desperately want our piece of it. There's no tomorrow, unless you create one for yourself."
South Africa's last World Cup defeat was by Australia in the 2003 quarter-finals and Deans insists the defending champions are adept at prevailing in pressure-cooker situations.
"South Africa still have the core group from the last World Cup together," he said.
"They know what it takes to be successful in knockout rugby and know how to close out the tight games.
"They've already shown that in this tournament when they came from behind to beat Wales by a point.
"They have a group which has the knowledge and belief that it can get things done.
"They will bring that mentality forward with them on Sunday.
"If we are going to earn the right to advance to the next round, we have to match it."
The Wallabies have been strengthened by the return of full-back Kurtley Beale and winger Digby Ioane.
Beale and Ioane have recovered from respective hamstring and thumb injuries, enabling Deans to re-select all but one of the XV that opened the tournament against Italy.
Pat McCabe, who has been in the treatment room with a shoulder problem, is selected at inside centre with Berrick Barnes dropping to the bench.
James O'Connor switches to the right wing with Ioane replacing Radike Samo in the number 11 jersey. Samo is restored to his preferred position of number eight.
Samo's return to the back of the scrum is one of five changes to the pack that helped demolish Russia 68-22.
Flanker Rocky Elsom, second row Dan Vickerman, tighthead Ben Alexander and loosehead Sekope Kepu are all reinstated.
"We've gone with the players and the combinations, which have served us best through the year to date," said Deans.
"Obviously injury and managing individual player work-loads has been a factor in selection through the tournament so far, but fortunately a lot of the injury problems that we've had are now behind us.
"The players that are coming back into the team after breaks are good to go."
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