'He's starting to believe he belongs at this level'

When champion batsman Michael Hussey retired in early 2013 he left behind a huge hole that has taken the Australian Test team five years to fill, but the wait has been worth it.

Besides his 79 Tests of experience, his role as leader of the team song and his terrific catching in the gully, Hussey was Australia's best No.6 batsman until Mitchell Marsh's Magellan Ashes reinvention.

Before Marsh's two Ashes hundreds, Hussey was the last player to score multiple centuries at four down for Australia in the five-day game, a stretch of five years and 53 Tests.

Marsh had batted at No.6 in 20 of those 53 matches before a chronic shoulder injury forced the allrounder into surgery, out of the Test team and unable to bowl for close to nine months.

In that time he worked on his batting with a focus on tightening his defence to match his already powerful attacking game, and the results have been spectacular.

Centuries in the JLT One-Day Cup, JLT Sheffield Shield and the Ashes were the fruits of his hard labour during the winter of 2017 as he patiently rehabbed his repaired right wing.

With the batting sorted he threw caution to the wind in late November and brought himself on to bowl ahead of schedule as the first Ashes Test was being played on the other side of the country in Brisbane.

He picked up two wickets in that Shield game and hasn't looked back to the point where he now claims he's bowling as fast as ever, and two Tests into the Qantas Tour of South Africa his teammates and Australian fans are seeing the potential Marsh has promised since debuting for Western Australia as a teenager.

With respect to England's wholehearted bowlers in the Ashes, South Africa's all-round attack is a step above, heightened by the advantage the hosts possess playing at home.

So while Marsh's 181 in Perth and 101 two Tests later in Sydney are clearly career-highs, his significant knocks against the Proteas in this series perhaps showcase his full development as top-order batsman.

Proteas great AB de Villiers said Marsh's 96 in the first innings of the opening Test was the difference between the two sides, after Marsh came in at 4-151 and guided Australia to a match-winning total of 351.

His 45 in the second innings at St George's Park isn't in the top half-dozen of his best scores, but it took two-and-a-half hours and 125 balls to craft against a fired-up Kagiso Rabada, the Proteas quick who had a reverse-swinging ball on a string.

That innings, along with Usman Khawaja's 75, ensured Australia put up a total for South Africa to chase, but it wasn't enough as Rabada eventually claimed the wicket of Marsh, who said some naughty words at the bowler as he departed that cost him 20 per cent of his match fee and one demerit point to his disciplinary record.

Couple those runs with two key wickets in South Africa's first innings and Australia not only have their most dependable No.6 since Hussey but an all-round package in the mould of Shane Watson.

Marsh's development as a bankable middle-order batsman and genuine strike weapon with the ball adds balance to Australia's Test XI that every selector, captain and coach around the world dreams of.

While Hussey has closely watched Marsh rise through the ranks, there is perhaps no better person who has witnessed the allrounder's evolution than his older brother Shaun.

"He's done fantastically well since he's come back in," Shaun Marsh says of his younger brother.

"I reckon it's the best I've seen him bat through his career. He's bowling well as well.

"He's getting better with each game he's playing with his bowling and we saw that in this game."

As good as Mitch is playing now, Shaun says the best is yet to come.

"There's definitely room for improvement for him and that's exciting for him and Australian cricket," he said.

"I think he's improving every game he's playing. He's really starting to believe he belongs at this level.

"It's great for him he's playing well and scoring runs and he's taking come crucial wickets for us now as well, which is really important as well."

The only thing holding Mitch Marsh back at the moment is a groin strain that he picked up in the second Test, but with 10 days between fixtures he's confident he'll be right to take his place at Newlands.

If Marsh is ruled out of the third Test, and that is a very big if at this stage, he would not only leave a hole, like Hussey did, at No.6 and as a fifth bowling option, but his leadership would be a blow to the tourists.

While Marsh was rehabbing his shoulder last year he was named captain of WA in place of retired skipper Adam Voges and brought his state immediate silverware by guiding his charges to the JLT Cup title.

As an Australia Under-19 World Cup-winning skipper, Marsh has captaincy experience from an early age, which is perhaps why assistant coach David Saker said on Sunday he's got the making of a future leader of the national side.

Shaun, who is eight years older than Mitch, says it has been odd taking orders from his younger brother playing for the Warriors but can see the leadership potential in him.

"He's growing in that aspect of his game," Shaun said.

"He's a really good leader amongst this group as well.

"He's got a good cricket brain and I think he's a natural leader."

Qantas tour of South Africa

South Africa squad: Faf du Plessis (c), Hashim Amla, Temba Bavuma, Quinton de Kock, Theunis de Bruyn, AB de Villiers, Dean Elgar, Heinrich Klaasen, Keshav Maharaj, Aiden Markram, Morne Morkel, Wiaan Mulder, Lungi Ngidi, Vernon Philander, Kagiso Rabada.

Australia squad: Steve Smith (c), David Warner (vc), Cameron Bancroft, Pat Cummins, Peter Handscomb, Josh Hazlewood, Jon Holland, Usman Khawaja, Nathan Lyon, Mitchell Marsh, Shaun Marsh, Tim Paine, Jhye Richardson, Chadd Sayers, Mitchell Starc.

Warm-up match: Australia beat South Africa A by five wickets. Report, highlights

First Test Australia won by 118 runs. Scorecard

Second Test South Africa won by six wickets. Scorecard

Third Test Newlands, Cape Town, March 22-26. Live coverage

Fourth Test Wanderers, Johannesburg, March 30-April 3. Live coverage