England were 333 for five in their second innings, a colossal lead of 566 runs, at stumps on the third day of the second Test at Lord’s on Saturday.
Root’s century, the second of his eight-match Test career, was exactly the kind of large or ‘daddy hundred’ so beloved of England batting coach and former Test opener Graham Gooch.
Ashes-holders England lost just two wickets in a near-ideal day for the hosts and, with so much time left in the match, the lack of a declaration from captain Alastair Cook was no surprise.
Long before Saturday’s close, Australia, bowled out for just 128 on Friday, needed to surpass the world record fourth innings winning total of 418 for seven made by the West Indies against them at St John’s in 2002/03 if they were to cause a stunning upset.
This was the 22-year-old Root’s first Test hundred as an opener after the Yorkshireman made 104 against New Zealand on his Headingley home ground in May.
That century, in a match in which then Test opener Nick Compton struggled, persuaded England to promote Root to the top of the order, where he bats for Yorkshire.
The selectors’ confidence in Root was justified by an innings spanning 110 overs and nearly eight hours at the crease that was a lesson in Test-match batting to Australia’s fallible top order.
Importantly, Root was not fazed by watching England collapse to 30 for three on Friday as Peter Siddle’s treble strike gave Australia a glimmer of hope.
“Last night was tough. They bowled exceptionally well and we knew we were going to have to scrap for a bit and earn the right to score runs later in the day,” Root told BBC Radio’s Test Match Special.
“I knew how hammering it home was important.”
He added: “It was pretty special, as a kid growing up playing the Ashes is the pinnacle, and to get a hundred and at Lord’s as well was a nice feeling.”
Together with Yorkshire colleague Tim Bresnan, who made an admirable 38 as nightwatchman, he put on 99 before sharing a fifth-wicket stand of 153 with first-innings century-maker Ian Bell (74).
Jonny Bairstow, another Yorkshireman, was 11 not out at stumps after helping Root add an unbroken 51 for the sixth wicket.
England, 1-0 up in the five-match series after last week’s 14-run victory at Trent Bridge, resumed Saturday on 31 for three, already 264 runs in front.
After two days of blazing sunshine, conditions were overcast for the first time in the match and offered a hint of swing.
But Root, 18 not out overnight, eased the first ball, from Siddle, through midwicket for four and was rarely troubled from then on.
And when he reached 70, Root became the first batsman this English season to score 1,000 first-class runs.
Bresnan batted solidly until he pulled a James Pattinson bouncer to Chris Rogers in front of square.
In a series already full of Decision Review System controversies, there was one more Saturday when Bell, on three, edged Ryan Harris low towards Steven Smith at gully.
Smith appealed immediately for a catch but, with the umpires and Bell uncertain, the decision was passed to third umpire Tony Hill.
As is often the case, replays were inconclusive and the verdict went Bell’s way.
Although 97 not out at tea, there were no nervous 90s for Root, who cut teenage left-arm spinner Ashton Agar for his 12th four to complete a chanceless 247-ball hundred.
Australia captain Michael Clarke, perhaps mindful of keeping his faster bowlers fit for future assignments, opted against taking the new ball.
Meanwhile Root, in a perfectly paced innings, upped the tempo with a succession of stylish boundaries.
Bell fell when he pulled Smith to Rogers at midwicket but Root put the leg-spinner in his place by pulling him for two sixes in three balls.