Roy's ton was big enough to end the hosts' proud home record of seven unbeaten ODI series wins in seven years. Bangladesh were bundled out for 194 in pursuit of 327, and it was Roy's innings that mainly put them out of the contest.
Roy got four boundaries with reverse hits off the left-arm spinners, apart from playing the conventional sweep to milk the slow bowlers.
"It was a plan [to sweep and reverse sweep] with the amount of turn," Roy said. "To go over point was the safest option for me. I tried to go over cover a couple of times, it was just too slow and too much spin. I tried to put that to bed quickly. Once Shakib [Al Hasan] gets that undercutter, I should have hit it to the sightscreen, but I tried to sweep him [and got out]. It was a slightly poor decision but apart from that, I think you had to keep your boundary options very simple. You can hit it wherever you want when you get a lot of runs. Out there, [hitting the sweeps and reverse sweeps] was one of the only boundary options for me today."
Roy said that the Dhaka pitch played to the batters' advantage. It was slow, but the spin was to a consistent degree, which allowed for easier strokeplay compared to the first ODI where the pitch offered uneven bounce.
"As far as skillset for batsmen, to score runs in these sort of conditions is as rewarding as it can get. I am very happy to score."
Jason Roy
"I only faced four balls the other day, it was clearly a lot easier today," he said. "But there was a bit more spin, but it was consistent. The other day it was slightly inconsistent bounce as well as turn. It was far lower scoring whereas today there was slow bounce. I think the boys showed a high amount of skill to give us that total."
Roy spoke about the relief of getting runs on this Bangladesh tour, particularly after getting out early in the first game.
"Every single time [scoring a hundred] means the world. I worked hard to right my wrongs from the first match. I made a silly mistake then, and I was hungry to make some runs. There are some hundreds in the past when you get to 40, and you feel really free-flowing when you get to the hundred. Every boundary was a scrap. I built a great partnership with Jos [Buttler]. We ticked over nicely.
"Every place poses completely different skillsets. None more so somewhere like here. I have scored runs in India. As far as skillset for batsmen, to score runs in these sort of conditions is as rewarding as it can get. I am very happy to score. The amount we scored today on that wicket in a series-defining match was awesome."
Roy said that he took a leaf out of Dawid Malan's book from the first ODI when the left-hander struck his fourth ODI hundred. It saved England from defeat essentially, as Malan mastered the conditions to take the visitors home.
"I have realised that very quickly once I stuck that one up in the air in the first game," Roy said. "The way Malan went about his innings, I quickly realised to switch on, put my head in and bat some time.
"It was just time at the crease. I can score a lot of runs if I batted that amount of time. As simple as that. I reduced the risk in boundary options. The one I got out to, was the highest risk for a boundary option I took. I got out stupidly."
Mohammad Isam is ESPNcricinfo's Bangladesh correspondent. @isam84