Root gives England some brief respite
Whatever the outcome of this Ashes series, Joe Root's 87 in the second innings at Adelaide will be seen as one of the game-changing innings of his career and one in which he came of age in Test cricket.
Root is 22 but appeared wise beyond his years from the moment he pulled on an England cap in India a year ago. There he batted for four hours to enable his side to get the draw they needed to win a series there for the first time in 29 years. Despite this being his 13th Test he still looks as if should be auditioning for the Milky Bar kid.
But while there have been callow moments, such as his ill-conceived dismissal in the first innings here when he was caught on the boundary sweep-slogging at Nathan Lyon, his second-innings knock was Test cricket in the raw, and a major turning point.
Coming in at 1-1, a score that went quickly to 20-2, against a fast bowler who has twice destroyed England's batting, is about as tough as it gets for a batsman in Test cricket.
Factor in England's low morale and the unfamiliarity of batting at No 3, following Jonathan Trott's sudden departure after the first Test, and it looked like the most brutish challenge of Root's short career.
Then there was the opposition's mounting bloodlust, in particular Johnson, a fast bowler intent on avenging five years of underperformance and ridicule against England, and on the rampage after dismissing Alastair Cook, England's captain, third ball.
It was a situation that gave off its own white heat but Root did not get burned, his resolve and compact technique able to ride Johnson's short balls and keep the feeding frenzy with which he devoured England's first innings at bay.
For two spells, Johnson hissed and glared as he sent down his missiles, but Root did not flinch. Instead, he gave Johnson that now cheeky smile of his, the one David Warner had tried to wipe from his face in a Birmingham bar last June.
That smile will now carry weight as he has confirmation he can play Test cricket despite falling 13 runs short of his hundred.
It would have been easy for Root and England to roll over after Michael Clarke had declared on Australia's overnight lead of 530.
But Root showed a resolve that has been lacking from some of England's senior players in this series, showing that while Johnson was always a handful, application and courage were practical antidotes providing you did not drop your guard against the others.
Having got through that, and another Johnson spell, he deserved a century but fell when Lyon turned one and he inside-edged it onto his pad, whereupon the ever-alert Brad Haddin made a good catch as it popped up on the off side.
England needed their senior players to scrap as hard as Root, and for a while Kevin Pietersen did, the pair adding 111 for the third wicket, which gave Cook's team their first respectable batting feat of the series.
Pietersen was dominant against the dolly mixtures bowled by Steve Smith, whom he struck for three sixes, capable against everyone else, but once more vulnerable against Siddle, his nemesis, for the second time in the match.
Siddle has now dismissed Pietersen nine times, more than any other bowler in Tests. His discipline and control of length preys on Pietersen's uncertainties. In the first innings he sprung a trap on Pietersen that Mr Magoo would have spotted, while in the second he forced him to play-on defending a ball with an angled bat.
Ian Bell, so dominant in the first innings, was more introspective here, eventually falling to Smith, toeing a full toss to Johnson at mid-on, who took a fine diving catch.
It was Smith's ninth Test wicket, and the third time he has snared Bell, a connection Clarke played on, just as he did with Siddle and Pietersen.
Australia's captain then caught Ben Stokes at second slip off Ryan Harris with the second new ball to leave England, who finished the day on 247-6, staring at the awful reality of going to Perth two down in the series.
While Clarke has enjoyed a fine Test from start to finish, Cook's has just got worse and worse. His dismissal in the second innings, caught at long leg top-edging a hook off Johnson, was him trying to assert himself without giving himself a chance, the bouncer being his third ball from Johnson. (© Daily Telegraph, London)