The pre-tournament favourites and host was on the brink of a surprising Cricket World Cup elimination, knowing victories against India - and then New Zealand - were virtually essential to book a place in the semifinals.
A string of unexpected defeats, defined by unsuccessful run chases, had a nation on edge, but on this occasion at least, against India, Roy and Bairstow had the chance to write the script. The chance to set the tone. The chance to keep England's World Cup dreams alive.
A breathtaking 160-run partnership in just 22.1 overs followed, the England pair negotiating its way through a tricky opening period before freeing the arms in the fashion fans have come to expect.
Roy, back from a hamstring injury, had the best seat in the house as a fired-up Bairstow thrashed 10 fours and six sixes in a scintillating 111.
Bairstow's opening partner fell for 66 but the damage was done, England pushing to a total of 337-7 that would prove far too much for India.
Another must-win match followed and so did a big opening partnership.
Roy (60) and Bairstow (106) added 123 in 18.4 overs on this occasion, again setting the platform for a 300-plus score that England's bowlers comfortably defended against New Zealand.
England then headed into a semifinal against the old enemy, Australia, with its mojo back.
And the attacking brand of cricket that saw England claim the world number one ranking in the 50-over format was on full display in that contest, too.
Roy and Bairstow faced a different challenge, chasing on that occasion, but the result was exactly the same: another 100-plus partnership in quick time.
Set 224 for victory, Roy was the main aggressor this time, walloping five sixes in a 65-ball 85 before an unjust dismissal. Bairstow added 34, too, as they wiped 124 from the target in 17.2 overs, effectively ending the game as a contest with a mix of timing, game awareness and, of course, customary aggression.
The contribution of new-ball bowlers Chris Woakes and Jofra Archer in England's recent resurgence cannot be denied, but it is Roy and Bairstow who have been the driving forces.
Of the 14 century-plus partnerships for the first wicket at the World Cup, Roy and Bairstow have provided four in just seven attempts. A 95-run partnership between the duo came in a clash against West Indies, too.
And the pair's importance to England was highlighted by the three matches that Roy missed. England lost two of those, stand-in James Vince and Bairstow combining for opening stands of 44, 1 and 0.
All of that means that the New Zealand camp will arrive at Lord's on Sunday having spent honours analysing, reviewing, fretting and plotting. Just how do they get Roy and Bairstow early?
England's success at the top of the order comes in stark contrast to New Zealand's early efforts with the bat.
The Black Caps has only produced only one opening stand of 100 runs or more at the World Cup, Martin Guptill and the now-dropped Colin Munro providing it against Sri Lanka in the third match of the tournament, almost six weeks ago.
Guptill and Munro combined for an unbeaten 137-run union on that occasion but the opening partnerships since - 35, 0, 12, 0, 5, 29, 2 and 1 - make grim reading for New Zealand fans.
Munro lost his place after a six-wicket defeat to Pakistan but his replacement, Henry Nicholls, has scored just 36 runs in three matches. Guptill, the leading run-scorer at the 2015 World Cup with 547, has managed only 167 in eight matches at the 2019 edition, and that tally includes a first-up 73 not out.
"No one is more frustrated than what I am," Guptill told 1 News.
The consequence of New Zealand's poor opening partnerships is an unhealthy reliance on captain Kane Williamson and, to a lesser extent, veteran Ross Taylor. And while the experienced pair have continued to dig their side out of trouble, another poor start in the final could prove costly.
Roy and Bairstow have provided England with an incredible source of momentum throughout this World Cup.
One more match-defining partnership from the pair will go a long way to helping England win the tournament for the first time.