Roy made 112 not out as he and opening partner Alex Hales (133 not out) set a new England ODI partnership record as they chased down a target of 155 and saw the team to a 10-wicket win in the second ODI at Edgbaston.
And Roy then followed that up with a stunning knock of 162 off just 118 balls at his Oval home ground on Wednesday as England got to a target of 208 in a shade over 40 overs to win the fourth ODI by six wickets and so take an unbeatable 2-0 lead in the five-match series.
But the series has seen him score 282 runs at an average of 141 and a strike rate of more than 122 heading into Saturday's finale in Cardiff.
"It was great to see, the way he went about it and the ruthlessness as well at the end, you could see by his reaction when he got out," Root speaking to Sky Sports in Cardiff on Friday, said of the 25-year-old Roy's innings at The Oval, which was just five runs shy of Robin Smith's all-time England ODI record score.
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England have become an increasingly bold side with the bat in ODI cricket following their tame first-round exit at last year's World Cup, with Yorkshire's Root now one of several top-order batsmen along with Hales and Roy capable of making significantly large hundreds.
"We've got a number of guys now who, if they get in on their day, will be lining up scores of over 200, which is frightening," said Root.