And the stakes just keep on rising. Ireland enter the Millennium Stadium this afternoon with destiny in their own hands and their title on the line.
Emerge unscathed and they're 80 minutes from Grand Slam immortality and a place beside Jack Kyle's 1948 and '49 team - the last Irish side to retain the Championship.
Defeat, however, opens up the race for the Six Nations again and hands all of the momentum to Wales going into the final day.
Warren Gatland's men will have enjoyed a build-up in which Ireland have been installed as favourites and lapped up the local media's ability to take umbrage at every throwaway comment in each column.
They'll reflect on their status as three-time champions and bulk suppliers to the 2013 Lions. Ireland may be the holders, but the Welsh feel like their trophy is simply on loan after an uncharacteristically fallow year.
They pack plenty of punch, but Ireland are an evasive opponent. Joe Schmidt's team come into this game with an enigmatic ability to switch tack just when they're in danger of being figured out, and they'll need every bit of nous to confirm their superiority.
On paper, the champions can be confident of winning an historic 11th successive Test: they are the form team, coached by a man who knows how to win and led by a wily and inspirational captain in Paul O'Connell, earning the 100th Ireland cap of an illustrious career.
Tournament leaders at the breakdown, their Lions half-backs are in excellent form, while they have beaten everyone bar New Zealand in the 16 games since Schmidt took over.
And yet, Wales will look at Jonny Sexton and Jamie Heaslip for signs of weakness. Can a hamstring heal in two weeks? Can a No 8 really reach the required intensity less than a month after cracking three bones in his lower back?
Ian Madigan is a fine player in his own right, but a recurrence of Sexton's injury before the game is dead would spell disaster for the visiting side. It's days like this when Schmidt needs his on-field voice and the Racing Metro man is the one player he can't do without.
He'll trust in the 29-year-old and his box-kicking partner-in-crime Conor Murray to put Ireland in the right places, but Wales' back-three are unlikely to be as accommodating as England's were a fortnight ago.
So, Ireland will need more from their ground-game.
At the Aviva Stadium, Schmidt opened his box of tricks but found Stuart Lancaster had done his homework. Shaun Edwards will have also prepared for the unexpected, but a step up in accuracy could just give Ireland the chink of light they need.
This could be the day where Ireland's relatively new-look centres get their hands on the ball. Wales' Jonathan Davies' tendency to rush up creates opportunities and the right pass can find space.
Despite facing an all-Lions back-row, Ireland will hope to win the breakdown battle by arriving early and delivering the ball quickly to Murray.
Their lineout is stronger than Wales', while the home side's front-row reserves look callow compared to the Leinster trio who will reinforce the Irish ranks around the 50-minute mark.
Much will depend on referee Wayne Barnes, who was a frustrating figure when in charge of Ireland's win over France last month.
Schmidt's side largely got on the right side of the English official while still giving away an above-average 11 penalties and the coach will have emphasised discipline all week. With Leigh Halfpenny around, cheap shots at goal are not advisable.
Wales will hardly be as ill-disciplined as they were last season, but they still live closer to the edge than Ireland. If the visiting side can handle the Welsh power-runners off first phase, then Gatland's side revert to their predictable phase-game. If that fails, they kick. If they're kicking, then Ireland will win.
All that is predicated on Sexton's hamstring surviving the pace. If he does, a third Grand Slam should be 80 minutes away.
Meanwhile, Andy Farrell has demanded England react to their setback in Dublin by keeping themselves in the Six Nations title race.
Scotland visit Twickenham today (5.30pm) in the penultimate round looking for their first victory at the home of English rugby for 32 years and a maiden win of the 2015 tournament.
A chastening 19-9 loss to Ireland has left England needing the champions to slip up against Wales if they are to seize a first crown under Lancaster and Farrell admits his players are determined to atone for an afternoon of disappointment at the Aviva Stadium.
"What happened against Ireland is a massive factor for this game," England's backs coach said.
"If you put that alongside the fact we are still in with a shout of winning the competition, then those two things together are a pretty powerful thing leading up to this game. Hopefully we'll put in a performance that matters.
"You learn a lot from a loss. Lads who haven't been in that type of position before will have learnt a lot.
"Did we let ourselves down against Ireland? We didn't play our best, but Ireland like most good sides have a way of making an impact on the game and they did that.
"There is a determination to put a performance in."
And Italy centre Andrea Masi has delivered a warning to France ahead of tomorrow's clash in Rome.
The Azzurri, fresh from beating Scotland at Murrayfield last time out, are chasing a third successive Six Nations home win at Les Bleus' expense.
"The first time (France) lost, in 2011, they thought it was just one of those things, but the second time gave them real doubts," Wasps back Masi said.
"A third time will show them that they have to change their attitude towards Italian rugby.
"But none of us would pretend that we are favourites for the game on Sunday. We may have earned a little bit of respect from France, but our objective is still to earn it for good."