Roy (180) breaks Hales' England ODI record (171)
Highest ODI score at MCG (beating Mark Waugh's 173)
Roy was reprieved by DRS on 91
England lead five-match series 1-0
Aus 304-8; Finch 107 (119 balls)
M Marsh 50, Stoinis 60
Image source, Getty ImagesAnd that is it from us on the day England got their first victory on their 2017-18 tour of Australia.
As I said back at 2:45 this morning, this is one-day series is the one everyone always cared about... right?
England take a 1-0 lead in this five-match series going into the second match on Friday in Brisbane.
Until then, goodbye.
#bbccricket
Steve Hodgson: England have scored over 300 runs but only two batsman have scored over 15. Root showing you don’t need to smash it around and Roy showing just how good he is at the start of an innings and that he can slow it down if needed.
James Taylor
Ex-England batsman on Test Match Special
England were hostile with the ball, which you don't always see in one-day cricket. We know what they've got with the bat - Liam Plunkett chipped in with a couple of wickets, and I thought Moeen Ali was outstanding today. With these short straight boundaries, he got the batsmen playing square of the wicket. Adil Rashid was expensive but he got crucial wickets at crucial times.
James Anderson
England fast bowler on BBC Test Match Special
Mark Wood set the tone for the match with his first ball - a bouncer to David Warner. I was delighted for him because he's had his injury troubles. When you've had ankle troubles as a bowler, slamming your foot down on that hard surface, you're always going to have doubts.
This day will be remembered for Jason Roy's incredible knock but don't forget the excellent role played by England's bowlers.
Mark Wood was excellent and showed the pace and hostility England have been lacking all winter.
England captain Eoin Morgan at the presentation: "It was incredible from Jason. It is quite evident that when he scores runs he is imposing at the crease. It is on the back of a tough summer but he finished it incredibly well. Now, what a way to start the series. There is a long way to go but it is a great way to start
"It really does surmise the character of the bloke. He was always part of our plans even when we left him out. We knew at some stage he would be part of our plans.
On Australia's total of 304, Morgan said: "I would have taken it at the start. 300 these days isn't that big a total to chase down. It wasn't a huge task. I have no doubt someone else would have put their hand up if Jason hadn't."
James Taylor
Ex-England batsman on Test Match Special
Jason Roy takes high-risk options, but he didn't get too funky today. He hit strong shots over long-off, long-on and cow corner.
Man of the match Jason Roy: "It was incredibly special. I don't have too many words right now. It is a huge honour to be out there for England again and to get runs on the board.
On beating Alex Hales' record ODI score for England: "He (Hales) wasn't too happy by the sounds of things. The first thing the boys said was about him being pretty disappointed.
"I am really honoured to be selected. It was a tough season last season so to be selected this time is incredibly special.
On reaching his century, Roy said: "I didn't know what to do I was so happy. It is my first time here - what an incredible place. We (he and Root) had good fun out there. He even started singing his own song."
Charles Dagnall
BBC Test Match Special
Jason Roy will have a lot of messages on his phone tonight - probably a few from the Sydney Sixers asking him where all his runs were when he was playing for them.
Roy made 62 runs in six Big Bash innings this winter, with a top score of 21.
Australia captain Steve Smith, speaking at the presentation: "Jason Roy played spectacularly well. He didn't give us a chance. He chanced his arm and it came off tonight.
"We left ourselves a bit short in the first innings. We lost wickets in the middle and it stopped us going as hard at the back end.
"We didn't start as well as would have liked with ball, they got off to flyer. It wasn't to be tonight."
James Anderson
England fast bowler on BBC Test Match Special
Ben Stokes would give balance to the side as an extra bowler - I wondered if they could have bowled Joe Root, as they had to bowl Liam Plunkett for four of the last eight overs. On another day, that could have gone disastrously wrong.
England limited-overs international Luke Wright: If England win this one-day series will county cricket get praised for producing these players or is county cricket and its players only mentioned when things go wrong?
James Anderson
England fast bowler on BBC Test Match Special
Even though the game had gone, Australia managed to impose themselves on Eoin Morgan and Jos Buttler with the hostile nature of their bowling.
Australia's total of 304 only ever looked like a par score at best but England made that look easy even with a little stutter at the end.
England fans have waited a long time for something to celebrate on this tour. Jason Roy has delivered and the victory gives England a 1-0 lead in this five-match series.
James Taylor
Ex-England batsman on Test Match Special
This England line-up is so destructive and skillful with the bat, they're a nightmare to play against and a treat to watch. Root was classy and clinical, and they played smart cricket throughout.
Here's a quick run through that record-breaking run chase for England.
James Anderson
England fast bowler on BBC Test Match Special
Less comfortable than most England players and spectators would have hoped for, but Jason Roy will take all the plaudits. You've also got to take your hat off to Joe Root for a serene innings of 91 without taking any risks.
England win in Australia!
Moeen Ali seals it with a crashing blow through long-on but this is Jason Roy's day. What a performance from him.
Now a single to Root. Over to you, Moeen.
One run to win.
Single to Moeen. He gets off strike.
Two runs to win.