Refusing to yield momentum, ruthless Australia is perfectly set for victory

Momentum, most agree, is among the most elusive psychological phenomena in professional sport. How to obtain and maintain the positive kind? How exactly to halt and reverse its opposite?

For three and a half days of this Durban Test, since Matt Renshaw began calmly pulling Australia's first innings out of the fire and seizing the game's initiative, Australia has stubbornly maintained control. South Africa, haphazardly, has failed to regain it.

Early on day four, Renshaw made a further mockery of the difficulties that have curtailed the progress of every other batter in this game — so far, none from either team has managed so much as a half-century — and belted 82 more precious runs in even time.

More absurdly still, as shadows covered the Kingsmead pitch late on day four, the burly Queenslander ripped one of his unheralded off-spinners out of the rough and removed Temba Bavuma, capping a horror game in which the Proteas skipper has been unable to buy a run and incapable of engineering the moments of inspiration his opposite number constantly pulls from his hat.

Could Bavuma have done much to drastically alter what has transpired here? Other than by contributing his usual runs, probably not.

He certainly can't grab the ball himself and rip through a middle-order batsman, as Pat Cummins did to Tristan Stubbs within sight of stumps.

Nor can Bavuma and his teammates always play out of their skins, above expectations, beyond their limitations, which has been the impossible task South Africa has pulled off, to the betterment of Test cricket, in the last two years.

That the home side enters the final day 319 runs in arrears with six wickets in hand is a testament to the chain of events a single player can set in motion, as Renshaw has in this game.

Only a few forced errors prevented Australia calling it a perfect day: looking less like a Test opener by the day, Travis Head fell cheaply again; thanks to a fast, frightful bouncer from the indefatigable Anrich Nortje, Steve Smith is being assessed under concussion protocols, which may imperil his selection for the second Test, although it did not stop him from using an iPad to assess the catching chances he missed out on as he sat in the pavilion.

Basically everything else about Australia's gung-ho approach worked out. To set a target as imposing as 421, they rattled along at 4.65 runs an over in the first session and a spirit-sapping 6.36 in the second, each batsman more enthusiastic than the last to attack at all costs.

Nic Maddinson clubbed an entertaining 46 to establish the launching pad. Smith and Marnus Labuschagne wound back the clock with a typically hyperactive partnership, the latter reaffirming the sense he has turned the corner. Towards big runs. Renshaw reprised his peak Matthew Hayden routine, toying with the South African bowlers. Even Beau Webster, previously out of sorts, made fluent runs too and could be permitted some frustration that the declaration halted his spree.

Cummins, in a contrasting cameo to his first innings vigil, hammered 32 from 12 deliveries, bombing Simon Harmer for a string of sixes that left South Africa dejected and dashed any remaining hope the off-spinner held of selection in the second Test.

The final effect of the Australian batting effort was something like a WCW tag team taking turns flying off the ropes with elbows extended.

All that now stands between Australia and certain victory is the solitary excellence of Aiden Markram, who always saves his best for Australia and finished the day undefeated on 45.

In the corresponding Test eight years ago, when the Cape Town fiasco was still on the horizon, Markram's epic century delayed Australia's victory in almost identical circumstances.

If the day was characterised by one team doing a bunch of things far better than its opponent, special mention must go to Josh Hazlewood for not just the most classically Hazlewoodian stat line — eight overs, three maidens, 2-20 — but for nipping out David Bedingham for 46, thus ending a 66-run second-wicket partnership with Markram that shaped as South Africa's last realistic chance of getting close.

Are Australians complacent about the unassuming New South Welshman and his mountains of wickets? Do we underestimate the problem it poses to batsmen when a 196-cm giant releases a heavy ball from that kind of stratospheric trajectory, lifting length balls into their ribs? How much harder is that to handle when, at the other end, the skipper skids it through lower, attacking the off stump from a different angle?

Probably it is the closest thing in the present era to what batsmen encountered four decades ago when Malcolm Marshall and Joel Garner combined to devastating effect for the golden-era West Indies.

Another good thing South Africa has given Test cricket in recent years is the guarantee of a result: not a single encounter there in the last decade has ended in a draw. Long may it be so.