JOE ROOT made Australia pay for dropping him second ball, with a counter-attacking century which transformed day one of the Ashes in Cardiff.

Root's seventh Test hundred, from just 118 balls and the fastest ever scored in the first innings of an Ashes series, was the driving force as England recovered from a perilous 43 for three to 343 for seven.

He shared an all-Yorkshire stand of 153 with Gary Ballance (61), and throughout helped England make good on their new commitment to an aggressive game plan as he and Ben Stokes (52) then took further toll of an off-colour Australia attack in a partnership of 84.

After Alastair Cook had chosen to bat on a cloudy morning, only to be the second of the early departures, Root survived nervous initial moments against his former county team-mate Mitchell Starc (three for 84) but was soon cashing in as conditions eased under ever sunnier skies.

The majority of his 17 fours were pedigree and trademark shots, often eye-catching square and cover-drives - including the one with which he brought up his hundred off Josh Hazlewood (three for 70).

Root (134) was putting behind him a rare double failure in England's last Test, on his home ground against New Zealand at Leeds, reprising a previous sequence of 11 half-centuries in 18 Test innings.

There was a touch of redemption too on his return to the Ashes fray after being left out for the final Test of England's 5-0 trouncing in 2013/14.

Good fortune also featured, most significantly when Root was dropped before scoring by diving wicketkeeper Brad Haddin off Starc - and he survived later scrapes against Nathan Lyon on 61 and 79, a DRS lbw procedure marginally going his way and then a possible inside-edge on to pad looping to short-leg where Steve Smith ought to have held on.

Ballance, back to form with his first half-century in any format for club or country since Grenada in April, operated in Root's slipstream en route to his milestone from 127 balls.

He did well especially to withstand a testing spell from Mitchell Johnson, who peppered the left-hander with short balls to a field of leg-side catchers from round the wicket.

England badly needed stability from the Yorkshire pair after their early troubles in which Hazlewood made short work of his fellow Ashes newcomer Adam Lyth, Lyon did likewise with Cook and Ian Bell's slump continued when Starc found telling swing in his second spell.

Lyth had tucked Hazlewood's fourth delivery off his pads for four - but trying to repeat the dose two balls later, instead got a leading edge low for a sharp catch by David Warner at gully.

Cook's evident attempt to take the attack to Lyon came to nought when he was undone by a little extra bounce from the off-spinner to be caught-behind cutting.

Bell made only a single, taking his sorry recent record to 56 runs in nine Test innings when he missed Starc's full-length swing to be lbw.

But Root overcame his scratchy start, a faint inside-edge on Starc's first delivery to him preventing lbw and then his most obvious escape thanks to Haddin.

Thereafter, he was soon playing with a convincing fluency as he and Ballance established a foothold before lunch - and then batted throughout the afternoon.

It was not until Hazlewood snaked one through to hit Ballance on the back pad that Australia had a breakthrough at last.

On a surface still providing the occasional hazard for batsmen and hope for the seamers, though, Australia could rarely exert control - and by the time Root finally edged an attempted drive to slip, at the start of Starc's seventh spell, it was symptomatic of the tourists' struggles that part-time medium-pacer Warner was eking out overs at the other end before the second new ball.

Stokes played across more Starc swing and was bowled off-stump, and it took a little of the Root gloss off proceedings for England when Jos Buttler chipped his wicket away to mid-on for a soft dismissal just before stumps.