South Africa ensured the Rugby Championship would go down to the final weekend following a comfortable win over a beleaguered Australia in Cape Town.

The Springboks stormed into a 20-3 lead after just 20 minutes to immediately kill off any threat from a Wallabies side desperate to finish a forgettable season on a high.

Adriaan Strauss and Zane Kirchner touched down in the immediate onslaught but crucially the Springboks failed to find the extra two tries they needed to secure a bonus-point success and make life easier ahead of their do-or-die clash with New Zealand in Johannesburg next weekend.

The All Blacks can move five points clear at the top with full points against Argentina on Saturday night - a result that would mean they need only deny South Africa a bonus-point win next week to retain the title.

South Africa had to wait until the 71st minute for their third try, Willie le Roux willing himself over, but a fourth was not forthcoming to leave a slightly bitter taste despite lifting the Mandela Shield.

Australia at least ended a mostly toothless display, that did improve after half-time, with a late try to debutant Chris Feauai-Sautia.

The Wallabies arrived in South Africa on the back of the controversy which saw James O'Connor left at home and looking to build on their first win under new boss Ewen McKenzie when they beat the Pumas in Perth last time out.

They were first on the board when Christian Leali'ifano steered home a penalty but from there South Africa took full control.

After Morne Steyn, who kicked a match haul of 15 points, levelled, front-rower Strauss bundled over for the first try on 13 minutes when Quade Cooper attempted to intercept rather than hold his position on the line.

Steyn converted and was soon sizing up another when Jean de Villiers' cut-out pass caught the Wallabies short on numbers out wide.

Le Roux made the break and fed the ball inside for Kirchner to race over.

South Africa had enjoyed 82 per cent of possession, and most of the territory, at that point and the game was virtually done and dusted when Steyn kicked over another penalty to make it 20-3.

The Springboks were effectively trapping Australia deep in their own half, with the visitors consigned to kicking the ball away to gain any relief.

Matters got worse, though, when Michael Hooper was yellow-carded for a dangerous tackle that sent Eben Etzbeth flying head over heels and prompted a scuffle the TMO was content to ignore.

Bryan Habana was denied by Adam Ashley-Cooper's try-saving tackle in the corner but Steyn kicked over a penalty to send his side into the break 23-3 up.

Flip van der Merwe did see yellow just before the break, after he led with an elbow that caught Joseph Tomane on the chin, and Australia sent on veteran Will Genia at half-time to try to make use of their man advantage after the break.

It failed to work as the match petered out, with the Springboks taking their foot off the accelerator.

Duane Vermuelen and Sitaleki Timani both spent time in the sin bin and it was only with nine minutes left that South Africa revived hope of a bonus point, when Le Roux forced his way over in the corner.

It was Australia, though, who got the fourth try when Cooper's cross-field kick, after a quickly-taken line-out, caught the Springboks out for Feauai-Sautia to stumble over.

Australia's performance, however, will no doubt raise concerns Down Under they could become Argentina's first victim since they joined the Rugby Championship when they travel to South America next week.