“Ask me at the end of the game,” said the Yorkshire batsman, the implication being that it would count for less if England did not go on to win the match.
Less than 24 hours later, England did go on to the win after one of the most dramatic day’s of Test cricket we have recently seen.
Resuming on 238-5 in reply to South Africa’s 313, they gained a first-innings lead of 10 before routing the hosts for 83 and completing a seven-wicket triumph to take the series.
Root conceded that it “possibly” was the best hundred of his career, with seven of his nine Test centuries having now come in a winning cause.
That speaks volumes for his ability to deliver when it most matters, and goes a long way to explaining why he is among the world’s leading five batsmen.
Root’s 110 at the Wanderers, which helped lift England from a precarious 91-4 in their first innings, was a masterclass of selective strokeplay.
The next-highest individual score in the match was 58 by Ben Stokes, with whom Root added 111 for the fifth-wicket in 15 overs in a stand that changed the momentum of the game.
If Root and Stokes laid the platform, it was Stuart Broad who sealed the 2-0 lead with one Test to play.
Broad’s remarkable return of 6-17 from 12.1 overs on Saturday afternoon – including a spell of 5-1 in 31 balls – was an inspired performance by someone who has a habit of producing such devastating bursts.
When Broad is hot, he is red-hot, and there are few bowlers who can match him for dramatic impact, his intervention here transforming a hitherto finely-balanced contest.
The Nottinghamshire fast bowler seems to have been around forever and a day, but, at only 29 years of age, he has plenty of time to go on and eclipse strike-partner James Anderson as England’s all-time leading Test wicket-taker, while there are few finer sights in cricket than to watch him charging in with his tail up.
On pitches that do a bit, like the one at the Wanderers, England are a highly dangerous proposition.
They are pretty good on all surfaces – apart, perhaps, from the ones recently encountered against Pakistan in the United Arab Emirates – and they have exposed a South Africa side who are on the way down, their batting weak and their bowling depleted.
The hosts went into the series ranked No 1 in the world, but, in reality, their results have been disappointing for some time.
Without their primary strike bowlers Dale Steyn and Vernon Philander, they do not have the impact performers like Broad who could have made the necessary difference.
England cannot yet be considered the finished article, but they are certainly on the way up and have a number of match-winning players.
It was widely accepted going into the series that they had four world-class players in the form of Root and captain Alastair Cook with the bat, and Anderson and Broad with the ball.
Now Stokes can be added to that number, while Steven Finn and Yorkshire’s Jonny Bairstow have taken great strides.
There are still question marks concerning Alex Hales at the top of the batting order and also the spin bowling situation, but few would deny that the signs are encouraging.
Above all, England are playing with what the coaches call “positive intent”.
Under Australian coach Trevor Bayliss, they have become an attractive side to watch, and, in men such as Root, Stokes and Bairstow, they have players who can draw in the crowds.
Much was made of England’s determination to play a more attractive style following the departure last spring of previous coach Peter Moores.
Although results have been inconsistent at times, England, aesthetically, have been true to their word.
There is also plenty of depth in the wings.
Chris Woakes did not play here, while Adil Rashid has been plying his trade in the Australian Big Bash, the Yorkshire leg-spinner being another X-factor player to throw into the mix.
England’s win at the Wanderers was helped by a pitch that was a magnificent advert for Test cricket.
Too many pitches these days are bland in the extreme, offering no proper contest between bat and ball.
At a time when Test cricket faces a battle for its future, with Twenty20 all the rage, it is imperative that the pitches – the most important factor in any game – are of excellent standard.
Few in this country would have been tuned into the Big Bash on Saturday morning when the Test match was in progress, because the cricket in Johannesburg was of such compelling character.
Eighteen wickets fell on what proved to be the final day, aided by some wonderful catching – not least by England’s James Taylor at short-leg.
There was lateral movement, which England exploited as eagerly as they did against Australia last summer, but there were also run-scoring opportunities for the batsmen.
Fittingly, the man who began the day looking to add to his ninth Test hundred from an overnight 106, was there at the end.
Root had added only four to that figure before he was caught behind early in the piece, but he clipped the winning run through mid-wicket in the second innings off Dean Elgar to spark great celebrations.