Root’s 107 was the first ton of the tournament and Buttler was in irresistible form with 103 in 76 balls, but both men fell before the finishing line, with Pakistan closing out a 14-run victory.
A target of 349 invited England to go where no other team had gone before at this level and while their master batsmen were in charge it looked as though they could, should and then would make it two wins from two.
But both departed shortly after reaching three figures, leaving too much for the lower order to do and confirming an improbable result for opponents who lost the recent series between the sides 4-0 and were fresh from a thrashing by the West Indies.
England will rue a shocking performance in the field, a litany of errors capped by Jason Roy’s drop of Mohammad Hafeez that ended up costing 70 runs, yet Root had just as much luck when he was shelled on nine.
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The 10-team format allows for setbacks such as this, but England’s hopes of building a head of steam have taken an early and unexpected blow.
In asking the opposition to bat first, Eoin Morgan clearly had designs on hustling the side who were blown away for 105 by the Caribbean quicks.
Pakistan rarely play to type, though, and gave a wonderful account of themselves.
An 82-run opening stand from Fakhar Zaman and Imam-ul-Haq saw off the new-ball charge and there were solid half-centuries from Babar Azam (63) and Sarfaraz Ahmed (55).
Best of all was Hafeez’s bright and breezy 84, a knock that raised the rate, forced bowlers off their lines and breathed anew after Roy fluffed the simplest of lines at mid-off.
In the absence of Liam Plunkett, dropped for Mark Wood, it took the off-breaks of Moeen Ali to hit back.
Fakhar was stumped as one spun past the edge and Imam holed out.
Woakes’s reaction to catching the latter was telling, the mild-mannered all-rounder raising his finger to his lips then jabbing it in the crowd’s direction. England might be at home, but they commanded no more than half of this diverse crowd.
Moeen and Woakes combined again to see off Babar, but Hafeez was the prize scalp in a final 10 overs that brought 96 runs and five wickets.
England might have settled themselves with a reminder that during last month’s ODI series they successfully chased 341 against the same opponents on the same ground.
Pakistan, meanwhile, had another precedent in mind. Noting Imran Tahir’s early dismissal of Jonny Bairstow at The Oval they opened with their own leg-spinner Shadab Khan and enjoyed similar rewards.
Roy was the man to go this time, lbw on the sweep in the third over, to complete a poor day at the office.
Had Root followed in single figures, as he should have, it could have been devastating, but when he edged Mohammad Amir to slip Babar fumbled.
For now, though, Pakistan were willing to absorb Root’s busy half-century and chip away elsewhere.
Bairstow nicked the explosive Wahab Riaz, England’s captain Morgan was bowled by Hafeez and opening-day hero Ben Stokes was suckered into an edge by Shoaib Malik.
At 118-4the scales were tilting hard against England, but Buttler was next man in.
He danced across his stumps to ramp Wahab, benefited from a couple of thick edges past slip and whipped Shadab for an effortless six to confirm a 34-ball fifty.
Root’s progress was simpler, threading the ball square on the off side and pulling whenever invited, and there was an inevitability about his hundred.
The acclaim was long and loud, but celebrated quietly in the middle, Root mindful of the task still ahead.
He was right to be wary, back in the pavilion six balls later when he sprayed Shadab to short third man.
The pattern played out almost identically in Buttler’s innings, a low-key acknowledgement as he roared to a fine hundred then disbelief as he chopped Amir to an identical fielding position.
Wahab ended the resistance, dismissing Moeen and Woakes with successive balls.
The writing was on the wall when Archer flashed Amir to Wahab coming in from the third man boundary though England at least avoided the ignominy of being bowled out, ending the 50 overs on 334-9.
A 14-run victory therefore went to Pakistan, who had their revenge for a 4-0 ODI series defeat to England last month.