Lydiate: Celtic tie to be decided in the back rock

History beckons for one of these teams and for the loser, a long journey home to ponder what could have been. Warren Gatland and Declan Kidney are both acutely aware this presents their greatest opportunity to take their teams to the semi-finals of the World Cup and, with France or England awaiting them, possibly beyond.

"It's all about knockout rugby," Gatland said. "The incentive is that whoever wins gets to stay until the end, but if you lose, you're going home on Monday."

Other than the All Blacks, these are the two most talked about teams in New Zealand, given Ireland's victory over Australia and their hoard of fans, while the Welsh style of rugby has attracted many admirers.

Tomorrow, however, will bear witness to their contrasting ideologies. Ireland have stuck to their tried and tested formula, as marked by the selection at fly-half of Ronan O'Gara.

"Ireland have a very experienced squad that have won a Grand Slam and Heineken Cups, but this is the World Cup," Gatland said. "They had a lot of criticism before but it doesn't matter if you lose warm-up games, it's about fronting up in the tournament."

Ireland's players have a track record for winning cup games at provincial level but have struggled to transfer that to international level. Wales have little cup pedigree and have instead opted for the confidence of youth, having left out Stephen Jones, Lee Byrne and Ryan Jones for Rhys Priestland, Leigh Halfpenny and Dan Lydiate.

"Both teams know each other very well but the Irish won't know as much about some of our younger guys," Gatland said. "They have no fear and we've encouraged them to have a go. "

George North is playing with the swagger of that new-found Welsh confidence but the epitome of Gatland's Wales is Lydiate, the 23-year-old farmer's son from mid-Wales who barely slept for 72 hours as he iced his ankle in a desperate effort to stay in the World Cup after injury against Samoa.

There are always games within games and the duels between Jamie Roberts and Brian O'Driscoll, or Tommy Bowe and Shane Williams, will fascinate. It is in the back row, though, where the game will surely be decided.

"Ireland have arguably the best back row in the tournament," Lydiate said. "[Sean] O'Brien is their go-to man, someone who trucks it up for them. It takes a lot of people to stop that but it's our job to try to nullify him." Both teams will be at full strength after Ireland hooker Rory Best was passed fit.