England at two occasions has missed the victory mark by a whisker despite reaching the final in front of their home crowd.
Root also suffered an injury scare when he damaged his calf early in his innings but he made light of the problem to post his highest one-day worldwide score.
England have also registered victories in eight of their last 10 ODI matches at the Oval; also, they claimed a 10-wicket win in the only previous such encounter against Bangladesh at the famous venue (June 2005).
After pre-match doubts over Stokes, who bowled seven overs and took England's first wicket, Chris Woakes became the latest injury-victim.
"The decision will remain the same throughout the tournament", he said.
Root never went for the big hits, but played smart cricket to ensure that the chase never comes under pressure.
"Alex Hales isn't going to score slowly. But I know that we finished on a high, and there were encouraging signs throughout the series and those are the kind of things we like to focus on", Sport24 quoted de Villiers as saying.
Bangladesh bowlers have not much to take back from the game as Mashrafe Mortaza and Shabbir Rahman could manage to pick one wicket each of the English batting.
The fact England chased down the runs so easily was a reminder that this will probably be a high-scoring tournament, so variety in your attack could be crucial. He combined for 166 with Mushfiqur Rahim, who was out for 79 straight after Tamim departed.
Tamim put on 166 runs for the third wicket with Mushfiqur, passing his ninth one-day global hundred from 111 balls as he paced an assault which brought Bangladesh 83 in the last 10 overs - despite the dismissal of both set batsmen to successive Plunkett deliveries.
It was left to Liam Plunkett to step up in his absence, taking 4-59 to put the brakes on the Bangladesh innings. The ball fell near him but Tamim had no idea where the delivery was and almost tripped on it, before it spun away.
But as the runs kept coming, an increasingly frustrated Stokes exchanged words with Tamim and mockingly patted him on the shoulder at the end of the 32nd over, with umpires Rod Tucker and S Ravi intervening to calm tempers.
Meanwhile a single against off-spinner Moeen Ali saw Tamim to his ninth ODI century in 124 balls, including 11 fours and a six.
Mushfiqur holed out in the deep next ball - and although Bangladesh still had the momentum to pass 300, it turned out their hosts had the measure of that target.
Having one opener in form certainly helped, Hales moving to within five runs of a sixth ODI century before he holed out attempting to slog sweep Sabbir Rahman out of the ground.
"Jason really epitomises the way we play; the aggression in which he plays, he always plays for the team, and he plays in a manner that is dictated with that".