Steve Smith dispelled doubts he was not ready for the top job with a century on debut as Test captain to swing the second Test firmly in Australia's favour on Friday.

Legendary Manchester United manager Sir Matt Busby's quote that "if you're good enough, you're old enough" rings true with Smith, who has vindicated the faith placed in him by national selectors.

The 25-year-old made a chanceless 133, becoming the ninth Australian to make a century on debut as Test captain and the fifth to do so in his first innings at the helm. His knock places him behind only Clem Hill, who made 191 against South Africa in 1910.

There must now be temptation for selectors to consider giving Smith the task of leading Australia to the World Cup if Michael Clarke does not return, though George Bailey has done an excellent job to lead the team to No.1.

Smith had said when he was announced as captain on Monday that he wanted to score runs, lead from the front then show tactical nous to enable Australia to take 20 wickets and win the game. He can now tick off the first two from that list.

If Australia's rejuvenated bowlers can dismiss India cheaply on Saturday, Smith could be in the position of hitting the winning runs on Sunday to give his team a 2-0 lead heading into Christmas.

Such a scenario seemed fanciful on Smith's first day on the job. But the rookie captain has responded to major challenges every day and emerged with his reputation enhanced.

He held his nerve and temperament on a gruelling first day when his bowlers wilted in the heat, and was rewarded the following day when his young attack fought back.

Then after his batsmen let him down he did as he promised upon accepting the job by scoring a bucket load of runs.

"That first day wasn't quite what I expected. It was one of the toughest days I've faced in captaining any team to be honest," Smith, who has captained his club, state and Big Bash League sides.

"I've really enjoyed the last couple of days. The boys have supported me really well."

These are heady days for the fresh-faced Smith, who in less than two years has gone from the fringes of the Australian team to become one of the biggest wickets in world cricket.

It took Smith until his 12th Test to breakthrough for his maiden century but when it rains it pours. Since the last Test of the 2013 Ashes in England, Smith has creamed 1262 runs at 70 with six centuries. He had scored 347 runs without dismissal this series until he chopped on Ishant Sharma.

Whereas in Adelaide his century consolidated the good work of David Warner, this time it was a game changer.

His team had been uncomfortably placed when he arrived at the crease on Thursday afternoon and plunged further into trouble when his lieutenant, Brad Haddin, departed.

By the time he walked back into the pavilion Australia was only 10 runs behind, the platform well and truly laid for a late assault from the tail.

The significance of Smith's latest century was apparent in the gusto with with he celebrated. His century in Adelaide was for the late Phillip Hughes, this was for the team, whom he acknowledged with several vigorous flourishes of the bat in the direction of the dressing room.

Smith later said his personal performance was irrelevant if the team was not playing well, a view Michael Clarke has held throughout his reign as captain.

It is not uncommon for batsmen lose their concentration upon reaching triple figures, even more so when they are as young as Smith, but the captain knew the job was not done.

Lunch was only several minutes away and the second new ball due not long after. Had he thrown his wicket away with a rash shot he would have undone a lot of his hard toil and exposed the Australian tail.

Rod Marsh's selection panel also deserves plaudits for showing the courage to throw the captain's blazer to such a young player. Only Kim Hughes and the late Ian Craig were afforded the honour this early.

Unlike his predecessors Mark Taylor, Steve Waugh, Ricky Ponting and Clarke, Smith had never led his country in the shorter forms of the game before getting the main gig. It seems not to have impeded him at all.