An opening stand of 174 between Roy (101) and Jonny Bairstow (79) kick-started England’s second-highest successful ODI run chase, before Jos Buttler (54no) joined in with a 28-ball 50 as they knocked off a ground record 310 for eight with more than five overs to spare.
Eoin Morgan’s men have a 4-0 series lead, despite centuries by Aaron Finch (100) and Shaun Marsh (101) and Travis Head’s 63 for Australia.
Roy set off with a glut of boundaries in an 81-ball century which contained 12 fours and was completed when he hoisted his second six high over long-on off Nathan Lyon.
Roy and Bairstow got out within nine runs and 13 balls of one another, Roy edging another attempted big hit at Nathan Lyon to short third man and Bairstow trying to guide runs fine on the off-side but too close to Tim Paine off the returning Billy Stanlake.
Joe Root was bowled as he tried to sweep Ashton Agar – who also had Morgan caught behind cutting.
Alex Hales was dropped by Paine off Michael Neser on 17 before Buttler took over with nine fours and a six to ease England to the win.
Finch’s 11th ODI century, and sixth against England, and Marsh’s second in three innings underpinned Australia’s total. Finch hit only six fours – and three sixes – in his 105-ball century, and Marsh mustered five, and four maximums, in his hundred from 91 deliveries.
Australia’s conservative approach, after Paine chose to bat first, appeared pre-planned on a pitch of fair pace but occasionally low bounce. The openers achieved six an over in the first powerplay, a rate they would not revisit until the innings was almost done, despite successive century stands.
Head got himself out, pulling Rashid to deep midwicket, and Finch fell to his very next ball after reaching three figures – lbw to Mark Wood.
Marsh was brilliantly caught on the long-on boundary as Roy made an interception and parried the ball 10 yards in-field to Craig Overton.
That put Willey on a hat-trick, and he picked up two more cheap wickets in the death overs as Australia fell perhaps a few short of their gameplan.