Sri Lanka had clearly resolved to try and push England a bit harder on a ground known for high scores but good intentions were no match for Jonny Bairstow's quick reactions in the second over. Danushka Gunathilaka dropped the ball down into the covers and immediately called his partner, Kusal Perera, through for one. Bairstow was far quicker off the mark - though Perera's running line was slightly obstructed by the bowler, Chris Woakes - and his scampering underarm throw caught the batsman inches short. Perera, who has been run out four times in his last 10 ODI innings, might have stood a better chance with a dive.
England chose to include two spinners, despite the poor forecast and a pitch that had sweated under covers, and it was hard not to have sympathy with Adil Rashid and Moeen Ali as they hugged themselves in the field and waited for the call. There was little for them in a true batting surface, either, but Moeen did get some heat into his fingertips when Gunathilaka drove uppishly back to the bowler's right. Moeen threw himself low to try and take a one-handed catch but the ball burst through his fingers and away - probably leaving his bowling hand feeling even more numb.
With a solid platform from which to attack England from at last, Dinesh Chandimal and Angelo Mathews came out swinging. Both smeared Moeen over deep midwicket, Mathews with a particularly brutal swipe into the crowd; but Chandimal upped the stakes a couple of overs later when he took on Liam Plunkett, giving the charge to an 86mph delivery and driving back over the bowler's head and into the second tier of the pavilion. Not content with making Plunkett look like a medium-pace trundler, he then jumped across to uppercut a short ball over third man to go to his half-century with another six.
Mathews's hitting during the closing stages ensured his side would soar beyond 300 for the first time in the series, particularly when he helped himself to 14 off the penultimate over, bowled by Plunkett. That included a sequence of three consecutive fours and it was one of his more deft strokes that stood out, as he contorted his body to flip a full, fast attempted yorker from around off stump clean over short fine leg, much to Plunkett's chagrin.
Jason Roy is the sort of opener who forces bowlers to wake up and smell the coffee whether they like it or not. He was well into his stride, having reached 50 from 39 balls, when Nuwan Pradeep began his fifth over. Pradeep began with a leg-side wide - although there was a suspicion Roy might have got a tiny edge on it - and was then subjected to a disdainful barrage of 6-4-4. The first was a crashing blow over long-on; the second dispatched through the covers with a fluid drive; the third clipped smartly off his pads as he walked across to make use of Pradeep's change of line. Up came the England hundred and a sense of the momentum shifting.
Gunathilaka had already made his third ODI fifty and picked up the second wicket of his short career when he latched on to what must surely be his best catch in a Sri Lanka shirt. Eoin Morgan connected well with a slash off Suranga Lakmal that looked set to give third man a test when a flying Gunathilaka intercepted it one-handed leaping to his right at backward point. Sri Lanka's catching has not been perfect on this tour but Gunathilaka's celebration in the direction of the dressing room suggested he has not been shirking.
Roy's hundred on his home ground was met with a rousing reception, as the crowd rose for a player much appreciated in these parts. Whether he took Chandimal's effort at endangering spectators in the pavilion as a personal challenge is unknown but the clean strike over the sightscreen off Seekkuge Prasanna in the 25th over, the ball ricocheting off the concrete steps, was as emphatic as anything seen all night.
Alan Gardner is an assistant editor at ESPNcricinfo. @alanroderick