Simon Katich says he is 'stunned' by Australia's team choice for the third Test against South Africa - adding that he can't understand what the selectors are trying to do.

Australia made four changes from their innings defeat in the second Test in Gqeberha, which levelled the series scores at 1-1 with one Test to play.

Scott Boland, Nic Maddinson and Beau Webster have all made way for Nathan Lyon, Cameron Green and Cooper Connolly, while Steve Smith ruled himself out on the morning of the Test through injury and has been replaced in the middle order by Josh Inglis.

Australia's latest team selection vs South Africa divides opinion

It is the makeup of Australia's batting line-up that has raised questions. Renshaw, who has been Australia's best batter on the tour and hit an aggregate of 272 runs in the first Test, has been moved back to open in place of Maddinson, having batted at five throughout the first two Tests.

Green, who would usually bat at number five, has replaced Smith at four, with Inglis promoted above wicket-keeper Alex Carey to bat at five. Among all that, amid question marks over his own place in the team, Marnus Labuschagne is ironically providing Australia with the highest level of consistency by remaining at number three. And Katich, who played 56 Test innings for the Aussies, has made his feelings clear.

Simon Katich criticises Australia, selectors over third Test calls

As well as the batting changes, there has also been significant criticism over the decision to drop Boland, who was comfortably Australia's best bowler in Gqeberha with figures of 5 for 82 in South Africa's only innings.

Speaking during the opening session of day one in Cape Town, which South Africa ended on 148 without loss after being put in to bat, Katich said on SEN Cricket: "On principle, the phone call should have been made to someone in Australia to send them over. To give them that flexibility.

"That would have given this team the flexibility of potentially having someone come in that's got some cricket and runs under their belt. Because the guys that they've got here in this squad, a number of them just don't have any first-class cricket behind them. So you're hoping that it works. And you cannot hope in Test cricket that you're going to do well.

"Two wrongs don't make a right, though," he said, referencing Smith's late withdrawal causing Australia to change their mind on batting first. "You can't hide... you can't put it off. You've got to get out there and face the music. You've got to get out there and face it. I'm stunned that they've gone down this path."

During play, Katich also made his thoughts very clear on his view of Australia's taking Boland out of the team in favour of deploying a spinner in Nathan Lyon.

"Dropping Scott Boland sends a bad message," he said. "It feels like it's the easy decision for them, rather than making the tough decision."