England's highest successful run chase in one-dayers was aided by some sloppy West Indies fielding and several dropped catches.
Chris Gayle had belted 12 sixes in his 135 to help West Indies to a daunting total of 360 for eight, their highest one-day international score against England.
The umpires had to replace the ball more than half a dozen times after several of Gayle's towering sixes landed outside the stadium, including one that measured at 121 metres.
West Indies smashed a word record 23 sixes in total. New Zealand held the previous record of 22 sixes, against West Indies in 2014.
Gayle was dropped on nine by Roy, who said the missed chance had been at the "back of his mind" when he took the crease.
"You want to step up a bit and do something good for the team," said Roy, who more than made amends by compiling his score in only 85 balls in a match-winning knock.
"It was a nice (batting) surface. We were chasing a big total, so it was quite daunting at the start."
Roy laid a foundation for Root to all but take England across the line with a stylish innings based on strokemaking and astute placement of the ball.
Root was denied hitting the winning run when he was caught on the boundary with the scores tied and left to a standing ovation.
Captain Eoin Morgan chimed in with 65.
"We went about the chase well, with a short side (boundary) and a howling wind," said Morgan, who felt the conditions and placid nature of the pitch had made the chase slightly easier than the target score.
West Indies captain Jason Holder lamented his team's fielding.
"We didn't bowl as well as we would have liked and didn't help ourselves in the field," he said.
"Our energy and body language in the field wasn't up to scratch today. We've got to pull up our socks."
The second match will be played on the same ground on Friday.
(Reporting by Andrew Both in Cary, North Carolina; Editing by Greg Stutchbury)
