Ryan McLaren (Getty)

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The enthralling series remains delicately poised at 0-0, with the Aussies under greater pressure to ensure that they field a side capable of finally doing the “20 wickets job” on the Proteas and winning -- only that result will see them knock the tourists off their No 1 spot in the ICC rankings.

South Africa could possibly afford to be a bit more batting-conscious in the choice of their XI, bearing in mind that another draw is enough to leave their status undisturbed for the time being.

Australia v South Africa 2nd Test Day 5 Highlights

Then again, that can be a fatal mindset: a stronger personal hunch is that the South Africans will be keen to show their truest colours, after being second best to varying degrees in the first two Tests, and strike out for a 1-0 victory to leave no doubt about their pedigree.

This being effectively the second of back-to-back encounters, with all the physical and emotional draining that accompanies entry into the last of them, how the respective brains trusts decide their combinations could be pivotal.

The Aussies, no doubt miffed and the more footsore side after their failed quest to knock over the Proteas in the 148-over fourth innings of the Adelaide Test in unrelentingly warm or hot conditions, are reportedly even contemplating a whole new front-line attack.

That is because the workload of Peter Siddle, Ben Hilfenhaus and even off-spinner Nathan Lyon was immense at Adelaide, and the three-day turnaround to Perth could have lingering repercussions from a fatigue point of view.

Smart money, I believe, suggests that at least two of those three will still play at the WACA, depending on the respective degrees to which the trio have bounced back physically by Friday.

Australia will also restore Shane Watson to a top-order position, giving their batting order a generally steelier look, although whether the eternally injury-prone all-rounder is able to make a bowling contribution remains to be seen.

But what will the Proteas do? There are heaps of permutations open to them, a situation complicated in no small measure by the readiness or otherwise of blue-chip player Jacques Kallis to assume his place.

Clearly they will do everything they can in frantic, physiotherapy terms to get him suitably ready to bat in Perth – he has had a sparkling tour thus far and sports an average of 75.

His impressive resistance in both innings at Adelaide suggests that he would probably be capable of doing so again at the WACA – Kallis appears to have an admirable pain threshold – but there is also the fielding matter to chew on: just how mobile can he be for the demands of diving, for instance, at slip?

Nicks tend to occur fairly frequently, and the ball also travels fast, in Perth, so you cannot really afford to carry a notably limping soldier (however brilliant his capabilities at full fitness) in the cordon.

I would suggest that the reprieve beneficiary, if Kallis is ruled out, will be the labouring Jacques Rudolph, dismissed four times in four knocks now by Lyon, but perhaps less likely to be troubled by him at the WACA, assuming the Australian “offie” even plays.

The Proteas arguably still need to do everything they can to field a spinner, for the key sake of variety and perhaps also containment ... and that man needs to be Robin Peterson rather than the shell-shocked, supposedly “attacking” leggie Imran Tahir.

They may opt for only four bowlers, and if all-seam is the call, Peterson might well miss out, which could prove an unfortunate decision.

My recommendation would be to play him anyway, even if it means that he has to bat a notch too high, perhaps, at No 7 in a line-up reassuringly still featuring Kallis among the established core of Proteas front-line batsmen.

But if Kallis is absent, and the out-of-touch Rudolph thus stays, the specialist batting department will contain some measure of vulnerability – enough to suggest that late tour call-up Ryan McLaren offers quite attractive shore-up possibilities in the lower middle-order.

 In a Kallis-less side,I would then be mightily tempted to employ this all-rounder (first-class batting average 30.57, highest score 140) at the expense of slightly unlucky Rory Kleinveldt, a solid “improver” in Adelaide although his bowling average in the series does remain an inflated 60.75.

McLaren would bat at seven, with Peterson then under a little less pressure at No 8, and also serve as seriously handy fourth seamer.

The 29-year-old McLaren has been in pretty decent form with both ball and bat as captain of the Knights in the domestic Momentum One-Day Cup, and performed more than respectably in his lone Test against England at the Wanderers in 2009/10, when the Proteas produced a muscular effort to win by an innings and salvage a 1-1 outcome from the four-match series.

These are the Proteas XIs I would recommend, depending on the great Kallis quandary; I believe they would offer enough depth and competence in both the batting and bowling departments:

Rob Houwing’s team if Jacques Kallis can play as batsman: Graeme Smith (capt), Alviro Petersen, Hashim Amla, Jacques Kallis, AB de Villiers (wkt), Faf du Plessis, Robin Peterson, Vernon Philander, Dale Steyn, Rory Kleinveldt, Morne Morkel.

Rob Houwing’s team if Kallis cannot play: Graeme Smith (capt), Alviro Petersen, Hashim Amla, Jacques Rudolph, AB de Villiers (wkt), Faf du Plessis, Ryan McLaren, Robin Peterson, Vernon Philander, Dale Steyn, Morne Morkel.

*Follow our chief writer on Twitter: @RobHouwing