Lydiate: Celtic clash will be settled in back row

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.

Twenty-four years after meeting here in Wellington in their very first World Cup fixture, Wales and Ireland come face to face looking to tread new ground again. Wales won that day and went on to finish third, their best showing at a World Cup, while Ireland have never reached the semi-finals.

"It's all about knock-out rugby," Gatland said. "The incentive is that whoever wins gets to stay until the end of the World Cup but if you lose, you're going home on Monday. There's no greater motivation than that."

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 bare 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. He is expected to kick the leather off the ball given the wind and rain that make Wellington's "Cake Tin" of a ground one of the most challenging in the world.

"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 the World Cup but it doesn't matter if you lose warm-up games, it's about fronting-up in the tournament and that's what they have done."

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 or history and we've encouraged them to have a go. We have a balance that we've not had before."

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, almost paralysed by a neck injury as a teenager, barely slept for 72 hours as he iced his ankle in a desperate bid to stay in the World Cup after injury against Samoa.

Such is the feeling of indestructibility within the Welsh squad after summer camps in Poland, where players were exposed to 5am training sessions and -140 degree cryotherapy chambers. Lydiate said: "Whoever we come up against, it's not going to be as hard as the sessions we did in Poland when the boys were all over the place, being sick. I guess that's why the management did it."

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. Sam [Warburton] is destructive at the breakdown and Toby [Faletau] is an awesome ball-carrier. It's going to be a great battle."

Both teams will be at full strength after Ireland hooker Rory Best was passed fit. Brian O'Driscoll said: "You have to do what gets you across the line, what wins games. It's about playing pressure rugby, not necessarily deciding on one type of brand before the game. A big factor too is going to be conditions and how much of an expansive game the weather allows you to play."