The hangover has lasted for four months, fractured snapshots of those Parisian nights coming crashing back into heads still aching with the foggy recollections of a golden chance missed.

For France and Ireland, the tales of the autumn were strikingly similar, so close; so far – two World Cup adventures set up for success prematurely ended by a single score. A bounce of a ball, a flip of a coin, a perfectly timed Cheslin Kolbe charge-down or Sam Whitelock jackal: for a third men’s World Cup in a row, France and Ireland’s final fortnight was spent as spectators.

These two were the defining sides of the last World Cup cycle, meticulously constructing a contender in the hopes of ending their tournament hoodoo. France coach Fabien Galthie and Andy Farrell, his Irish counterpart, identified areas in need of improvement and duly improved them, bringing through key personnel and developing depth. They entered, and exited, the World Cup with few apparent weaknesses; either would have been a worthy winner.

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Both came up short. "Four years of consistent progress, the only objective was to be world champion,” Galthie said late last year. “One point is nothing, but one point is everything. We’ll be scarred for life and that’s part of our journey.”

And now it is time to pick up the pieces and start all over again with a fresh challenge. It feels fitting for these two to hit the rest button on men’s international rugby with the first fully-fledged fixture since the World Cup’s conclusion, and a Six Nations opener that may yet prove this year’s defining, deciding game.

This clash of grand-slam champions will feel somewhat fresh. Partly, that is due to a new amphitheatre, the impending arrival of the Olympics in the French capital necessitating a shift south from the Stade de France; Marseille’s Stade Velodrome is a wondrous sporting cathedral and a fitting stage.

But the sense of the nouveau is best identified in the spaces left by those no longer here. Johnny Sexton and Antoine Dupont were the faces of their nations, primordial to the projects upon which they embarked and the embodiment of the rugby philosophies around which these two were sculpted.

Sexton has for so long been central to this Irish side, both its backbone and its brain. Careful management enabled Farrell to eke out the last drops of an outstanding vintage, but in doing so perhaps stalled the progress of a successor. Jack Crowley’s emergence, then, is timely, the Munsterman having kicked his province to United Rugby Championship victory last season and now ready for his international chance.

“I think it’s got to happen organically; it’s got to be genuine,” said Crowley of how he will step up with Sexton gone. “For me, it’s been trying to learn so much from Johnny over the last two years and absorb as much as I could. I need to grow and understand myself and my game and how I can impact this group.”

Peter O’Mahony’s elevation to the captaincy should ensure a steady, disciplined ship. The blindside remains one of Ireland’s best at 34 years old, though the peculiar reluctance of the Irish Rugby Football Union (IRFU) to hand their new skipper a central contract has put Munster in a bind with O’Mahony up for renewal. The flanker has insisted his full focus is on this campaign but the sort of club/country tensions avoided in the last cycle threaten to bubble in the background.

That much is true of France, too, where the alignment achieved in the build-up to a home World Cup seems to have been rolled back slightly. The Top 14 clubs were generous in making their players available ahead of that tournament, but a complex system has been settled on for this campaign that sees much more to-ing and fro-ing of fringe squad members, which would seem to suit no one.

Dupont will be back after the Olympics but his departure to the sevens circuit leaves even this remarkably gifted French side seeking a new nucleus around which their free electrons can whizz. Romain Ntamack, his running mate, remains out, too, so it is fortunate that Fabien Galthie can count on a club pairing in red-hot form. Maxime Lucu and Matthieu Jalibert are joined by fellow Bordeaux-Begles Yoram Moefana, Louis Bielle-Biarrey and Damian Penaud in the French 23 with no side playing better attacking rugby in Europe this season.

The pieces elsewhere, largely, remain the same for France, though it is a shame that the kaiju Emmanuel Meafou will have to wait for an international arrival due to injury. Galthie can at least call on the colossal Uini Atonio and Romain Taofifenua, who postponed planned international retirements after the World Cup, to help compensate.

That both coaches have opted for six forwards on the bench speaks to an expectation of another bruising battle. The Stade de France is far from staid but when France visited Marseille in the autumn of 2022 to encounter South Africa, the atmosphere was positively febrile, and the Friday night lights should give this opening game a real sense of occasion. There are plenty of courses to be served in this Six Nations but this is not your traditional appetiser.

“We all know it’s going to be a war of attrition,” said Farrell on Wednesday when unveiling his team. “It’s mouth-watering, isn’t it? The stadium, the atmosphere, it being the first game of the Six Nations after a World Cup, if you can’t get excited about that, you’re in the wrong place.

“For us, it’s just living up to our own expectations, we expect to perform on the big stage and it doesn’t really get any bigger than this one. We’ve got to relish these types of occasions and go after them.”