Ireland head into their quarter-final against Argentina on Sunday as the Northern Hemisphere's best hope of having a participant in the last four.
Scotland will give it a go, Wales will be competitive and France either abysmal or sublime (maybe even a combination). Ireland though are in a different boat.
Last week's win over France was comprehensive, in spite of those injuries to Johnny Sexton, Paul O'Connell and Peter O'Mahony – with the latter two proving to be catastrophic blows.
O'Connell had to watch on from the sidelines as the British and Irish Lions won in Australia two years ago, but this is different, the end of his career with Ireland in the most wretched circumstances.
Much like Brian O'Driscoll he has been respected the world over as one of the premier players in his position, and Ireland will miss his leadership.
He has been a warrior, a giant of the sport admired by millions. Players like O'Connell don't crumple to the ground unless it's something bad, as you knew it instantly was last Sunday. Ireland now have to move on without him.
Not that it seemed they missed him too greatly against a hapless French side who lost their way in the second half. Iain Henderson has enough bite to his game to fill O'Connell's sizeable shoes, impressing off the bench last weekend, but even though O'Connell will be missing from the engine room the biggest area of interest is Ireland's back row.
O'Mahony's injury and Sean O'Brien's one-week suspension for his punch on Pascal Papé leaves Joe Schmidt without his first-choice flankers.
Chris Henry is a natural, reliable replacement for O'Brien at seven, but the contention is on the other side.
Henderson has the flexibility to shift there if Ireland had wanted to play Donnacha Ryan at lock, but Jordi Murphy wins the spot – the Barcelona-born back-rower who started twice at number eight during the 2015 Six Nations against Italy and England. Opting for that trio reunites the same unit who took on Romania at Wembley, but this will be a much bigger challenge.
Argentina have flown under the radar somewhat since they made New Zealand sweat in their opener last month, picking up three straightforward wins over Georgia, Tonga and Namibia by a combined score of 163-44.
Daniel Hourcade has worked hard to supplement their trademark power with more cutting edge out wide, and the results are beginning to appear.
Defeating South Africa in Durban earlier this year was another stride forward, and another sign that they belong in the Rugby Championship.
Juan Imhoff and Santiago Cordero have finished the pool stages with three tries each and they've done it with some swagger. Being able to combine that flair with their power up front is a bonus, although play too loose and they'll fall into Ireland's hands.
Argentina will want to attack through their scrum, but they have to maintain their defensive shape over multiple phases along with their discipline. Jérôme Garcès penalised them frequently in that game against New Zealand.
When it comes to World Cups for Argentina the heroes of 2007 are tough to match but eight years ago Argentina were a surprise package. Now, after four years at the Southern Hemisphere's top table, there are expectations.
Twice before in 1991 and '07 have Argentina ended Ireland's World Cup hopes, albeit never an Irish side as good as this one. It's an incredibly tight one to call.
Ones to Watch
For Ireland: That high number of injuries might have made Schmidt re-think his approach for Sunday. Ireland haven't truly unleashed their maul yet but this feels like Devin Toner's time to step forward. The 208cm lock looks set for a big day at the lineout with O'Connell gone, but he has stepped up in big matches recently for Ireland. Cardiff could be his time. Jamie Heaslip also has a massive role to play as the only surviving player from last week's back row and as Ireland's new captain.
For Argentina: Marcelo Bosch's suspension deprives los Pumas of a class act in midfield and also a long-range goalkicker over 50 metres, putting the pressure onto Nicolás Sánchez. The top points scorer in the 2014 Rugby Championship has 51 points to his name so far in this Rugby World Cup, including nine penalties and a drop goal, and every attempt will be crucial this weekend.
Head-to-head: This one could hinge on the scrum. Mike Ross continues to battle away in the front for for Ireland with performances to defy his critics ahead of turning 36 this year. There's little that Ross hasn't seen by now at the top of the sport, but that doesn't mean that handling Marcos Ayerza is an easy task. The best loosehead on the planet has shown no signs of slowing down and will do his best to get stuck into Ross from the first engagement.
2014: Ireland won 23-17 in Tucuman
2014: Ireland won 29-17 in Resistencia
2012: Ireland won 46-24 in Dublin
2010: Ireland won 29-9 in Dublin
2008: Ireland won 17-3 in Dublin
2007: Argentina won 30-17 in Paris
Prediction: Mightly close across the board, with Argentina's side looking impressive as they return to their strongest XV. Having Jonathan Sexton available, if he's fully fit, might just be the difference in what has the potential to be the game of the weekend. Ireland by 5.
Ireland: 15 Rob Kearney, 14 Tommy Bowe, 13 Keith Earls, 12 Robbie Henshaw, 11 Dave Kearney, 10 Johnny Sexton, 9 Conor Murray, 8 Jamie Heaslip (c), 7 Chris Henry, 6 Jordi Murphy, 5 Iain Henderson, 4 Devin Toner, 3 Mike Ross, 2 Rory Best, 1 Cian Healy
Replacements: 16 Richardt Strauss, 17 Jack McGrath, 18 Nathan White, 19 Donnacha Ryan, 20 Rhys Ruddock, 21 Eoin Reddan, 22 Ian Madigan, 23 Luke Fitzgerald
Argentina: 15 Joaquin Tuculet, 14 Santiago Cordero, 13 Matías Moroni, 12 Juan Martín Hernández, 11 Juan Imhoff, 10 Nicolás Sánchez, 9 Martín Landajo, 8 Leonardo Senatore, 7 Juan Martín Fernández Lobbe, 6 Pablo Matera, 5 Tomás Lavanini, 4 Guido Petti, 3 Ramiro Herrera, 2 Agustín Creevy (c), 1 Marcos Ayerza
Replacements: 16 Julián Montoya, 17 Lucas Noguera, 18 Juan Pablo Orlandi, 19 Matías Alemanno, 20 Facundo Isa, 21 Tomás Cubelli, 22 Jerónimo De La Fuente, 23 Lucas González Amorosino
Date: Sunday, October 18
Venue: Millennium Stadium, Cardiff
Kick-off: 13:00 local (12:00 GMT)
Referee: Jérôme Garcès (France)
Assistant Referees: Romain Poite (France), Chris Pollock (New Zealand)
TMO: George Ayoub (Australia)