Both average well above 50 in tests, with Smith ranked as No1 by the International Cricket Council and Root No2.
They both direct proceedings from second slip, and bowl some occasional spin. For both it is their first Ashes series in command.
Their backgrounds are remarkably similar generally and specifically. Smith comes from Sydney, where Australian cricket began, Root from Yorkshire, where professional cricket took off in the 19th century: both grew up in their country's cricketing epicentre, with all the habits of best practice ingrained.
Specifically, Smith and Root were trained from a early age by their fathers, with the aid of a cricket ground close to the family home.
Root was one-day-old when he first held a cricket bat, albeit made of cardboard, and was batting in the garden as soon as he could toddle against the bowling of his father, Matt, who played for Sheffield Collegiate.
Smith's father, Peter, went a stage further and learned how to bowl every type of right-arm delivery so Steve could practise of an evening, both in the family garden and at Casuarina Oval in Sydney.
Smith was habituated to hit along the ground because of the flower beds, and because Sir Donald Bradman said you cannot get out if you hit along the ground.
Root was stretched by playing from the age of 10 among men for Sheffield Collegiate, inspired by the club member Michael Vaughan who captained England.
Smith rose quickly through the sides at Sutherland and at 15 was opening their batting with Phil Jaques, who opened for Australia. Neither completed his secondary education because cricket was so obviously going to be their livelihood, and soon: both made their test debuts aged 21.
Going into this series, Root as captain has won five and lost two of his seven tests, while averaging 60 with the bat.
Smith has won 13 and lost eight of his 26 tests, averaging 69. If this is another respect in which Smith appears to be half a step ahead, largely because he is more senior, he has a distinct advantage in what is widely considered to be the decisive battle-ground of this series.
His four main bowlers have taken 257 wickets in tests in Australia at little more than 30 runs each. Root's five main bowlers have naturally taken fewer wickets in Australia, 66, at an average nearing 40.
In these last hours before the Ashes, Root can realistically hope that Australia's advantage in bowling — based on their superiority in pace if not statistics — may not take immediate effect.
Given the forecast of heavy showers interspersed with sub-tropical sunshine, the greenish Gabba pitch may continue beyond the opening session to be "a deck" of the kind beloved of English seamers, who excel in patient line and length: in which case the source of Australia's unbeaten record in Brisbane for almost three decades could be turned into their weakness.
To blunt Australia's bowlers, nobody is better equipped than Root's predecessor. If Alastair Cook can wind his clock back to 2010-11 and make three centuries in this series, he can be expected to take down one if not two of Australia's seamers — and the reserves behind Mitchell Starc, Josh Hazlewood and Pat Cummins are no better than England's finest in Australian conditions, if their equal at all.
But however good Root may be at the form of poker that is a press conference, he cannot pretend that his hand is as strong as it was last summer. He was blessed then with three world-class all-rounders.
Of them, Ben Stokes is in England, for a while; Moeen Ali has yet to face a single ball of pace in a game on this tour; and Jonny Bairstow, who did not face any pace in England's last warm-up, finds himself at No7, charged with the task of protecting a tail which could go up in a puff of smoke, such is Starc's expertise with the reverse-swinging yorker.
Psychologically, though, England for once in Brisbane are "good to go" as Australians say.
If Smith holds the advantage in several particulars, Root has a head start in that England hold the Ashes, and therefore will retain the urn if they can force a series draw.
Five key questions for series
1. Can the Poms handle the Aussie heat?
No, not the weather, but the heat generated by Australia's pacemen. Mitchell Starc and Pat Cummins can both clock 150km/h while Josh Hazlewood is slippery enough. Much of England's batting line-up is short on test experience against genuinely fast bowling. How they handle the quicks could decide the series.
2. Can Australia's new chums fire?
Opening batsman Cameron Bancroft, the inconsistent Shaun Marsh and gloveman Tim Paine face stern tests of their technique and character. All were somewhat controversial selections. If they fail to make an imprint early in the series, how long will they be given to settle?
3. Who will rule the captaincy duel?
Steve Smith and Joe Root are world-class batsmen who will be hunted by opposition bowlers. If either fails, their nation might go down with them. Both are renowned as aggressive skippers and their tactical nous in pulling the right strings at the right time is almost as vital as their run-scoring.
4. Will allrounders or specialists prevail?
England's Chris Woakes, Jonny Bairstow and Moeen Ali are cherished for their allround talents but Australia have ditched their desire to find an allrounder, picking only specialists. If the home nation's frontliners can't do the job, will they be lacking left-field options to turn a game?
5. Will injuries play a part?
Many pundits predict fast bowlers will decide the series. Australia's pace attack of Starc, Hazlewood and Cummins are feted but all have long injury histories. England spearheads Jimmy Anderson and Stuart Broad will carry the tourists' attack, but can the veterans survive and flourish in five-straight tests?
- Telegraph Group Ltd & AAP
