With thoughts turning towards next year's World Cup, Eoin Morgan's last-minute back spasm which ruled him out of the match in Cardiff provided a useful experience for England in a scenario that could play out during the tournament.
Batting first, England put a mammoth total of 342 in reply to which Australia could only manage 304 runs.
There were concerns that Australia, under the leadership of new captain Tim Paine, might face a barrage of abuse from England fans during the first ODI at The Oval on Wednesday. "Just the way I knuckled down early, it was quite hard and I went through some hard patches but then came out the other side".
Roy was eventually dismissed during an eventful 36th over.
Roy, dropped by England for last year's Champions Trophy semi-final on this ground, was back at Sophia Gardens less than two weeks later in a Twenty20 global against South Africa.
Sweden bury World Cup opening jinx to beat South Korea
South Korea's World Cup team responded to a Swedish spy for Sweden's team by swapping their jerseys so it would be harder to tell them apart.
"I was able to knuckle down and get myself in", Roy said.
It was a mature display from Roy, who said he was particularly happy with the way he had paced his innings and changed through the gears. "I wouldn't say being dropped in that Champions Trophy has anything to do with making any hundred feel any better than the next".
"It was a big aim for me to come after a long winter and to start well on home soil".
Just prior to this current series, England suffered a shock six-run defeat by Scotland in a stand-alone ODI in Edinburgh.
But if Australia dared to breathe a sigh of relief, having put England in on a cloudy morning, it did not last long thanks to Buttler - who hit two successive trademark ramp-shot sixes off the pace of Jhye Richardson to kickstart a predictably manic last 10 overs with one which cost 20 in all. "It's bittersweet", said Marsh. "It's nice to get a few runs but, yeah, I was obviously disappointed with the result".
Australia have just a few days to regroup before Tuesday's third ODI in Nottingham, where another defeat would give England an unassailable 3-0 series lead.
Australia were not much better themselves, it was a poor game.