South Africa were 67 for two at lunch after new captain Jacques Kallis won the toss and decided to bat here on Friday.
Kallis was unbeaten on 14 at lunch, while Boeta Dippenaar was on 21.
Australia, who won the first two two Tests, named an unchanged team for the third successive match but South Africa were without regular captain Graeme Smith, who suffered an injured left ring finger during fielding practice Thursday.
Kallis became South Africa's 31st Test captain.
Smith was diagnosed with a severe soft tissue injury and will wear a splint for 10 to 12 days.
Gibbs was promoted to open the batting with AB de Villiers, while Dippenaar batted at number three.
De Villiers and Gibbs made a cautious start and the first four overs from Brett Lee and Stuart Clark were maidens.
After an hour of restraint, De Villiers played a loose drive against Clark and was caught at cover for 12.
Gibbs followed three overs later when he left a ball from Michael Kasprowicz, which cut back and hit his off stump. It was the eighth time in 11 innings that the out-of-form Gibbs had been bowled.
Dippenaar, in his first Test of the summer, looked solid as he and Kallis batted through to lunch.