Eoin Morgan’s team did all the hard work by restricting Sri Lanka so effectively to an under-par 254 for seven on a decent pitch, and then needed mere competence in the run chase.
Hales (133no) and Roy (112no) were intent on doing the job in style, though, the former celebrating his 91-ball century by adding – to the nine fours and three sixes already hit – three more maximums in successive balls in a Seekkuge Prasanna over which cost 27 runs.
Mercifully for Sri Lanka, if alarmingly too, the battering was complete 15.5 overs early – Roy having reached his hundred, too, with his fourth six to add to six fours, from one ball more than his partner, as England surged to an early and highly emphatic win.
They were rewarded not only with a 1-0 Royal London Series lead but – after Tuesday’s tie at Trent Bridge – also an unassailable 13-3 advantage, and therefore victory, in Andrew Strauss’ inaugural cross-format Super Series.
After the rollercoaster events in Nottingham, replete with Liam Plunkett’s last-ditch score-levelling six, Birmingham served up a mis-match.
It was witnessed again by a sell-out crowd, 23,000 of them this time, a naturally partisan gathering who lapped up England’s supremacy.
Umpire Bruce Oxenford had taken the precaution of carrying a protective arm-guard, the first time an on-field official has done so in an international match – although John Ward wore a helmet in Canberra earlier this year.
The Australian, it turned out, was not in the firing line.
But Sri Lanka’s stand-in wicketkeeper Kusal Perera was given good reason to repent at leisure the untidy work which twice – if one down the leg-side were bat rather than pad – reprieved Hales off Farveez Maharoof when he had made only six.
Either way, it became men against boys as realisation came quickly that the target set was woefully short of defendable – and England’s openers helped themselves.
Hales, recording his sixth half-century in his last seven one-day international innings, went on to his third hundred in this format and Roy his second.
For good measure, after Hales was badly dropped at point by Danushka Gunathilaka on 126, former captain Strauss’ stand of 250 with Jonathan Trott against Bangladesh at this same ground six years ago was ousted as England’s best for any wicket in ODIs.
After Angelo Mathews had chosen to bat, Sri Lanka were never able to achieve the momentum he must have anticipated after passing a late fitness test on his sore hamstring.
They were hampered to an extent by what seemed to be a similar injury to Dinesh Chandimal (52), who twice needed treatment on the pitch during his painstaking 86-ball innings and later had to give up his wicketkeeping duties.
Upul Tharanga’s 46-ball half-century did provide a much-needed flourish of 44 runs from the last four overs, but to little avail.
Plunkett was in the attack early, after Gunathilaka had taken on David Willey and deposited him for two sixes in three balls – over long-on, then long-off. The left-hander then tried another booming drive to the first delivery he faced from Plunkett, and paid the price caught-behind.
Kusal Mendis went back to a ball that was slightly too full and went lbw for a duck to Plunkett, and Perera was well short of his ground when Roy ran him out with a direct hit from point.
Chandimal and Mathews shared a stand of 82 in 16 overs, until the captain mistimed an attempted sweep at Adil Rashid to dolly a catch to short fine-leg. Rashid, who again bowled well as at Trent Brige, was rewarded with a second wicket in three balls when wild-card hitter Prasanna got underneath an attempted big hit which was mis-judged but very well-held by Willey at a straight mid-on.
Chandimal completed his half-century with 14 consecutive singles, among 27 in succession as Sri Lanka struggled from 146 to 173.
When Chandimal’s bid for yet another minimum instead saw him run out in a mix-up off the last ball of the 40th over, the tourists were 188 for six.
Against opponents who always seem to bring out the best in him, Tharanga (53no) hit five fours and a six as his unbroken partnership of 63 with Suraj Randiv at least got Sri Lanka past 250.
If that saved some embarrassment, the effect did not last long.