Pivotal figures: O'Brien and Warburton

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• Ireland
• Wales

Also see

• O'Driscoll not looking too far ahead
• Welsh Wizard not done yet

Saturday's World Cup quarter-final between Ireland and Wales is a clear example of just how much can change in a month.

Heading into the World Cup Ireland were at a low, a team struggling to find their feet despite obvious class. Declan Kidney's men didn't get their tournament off to the best start either with an unconvincing win over the USA.

But then came Australia.

With a surprise win over the Wallabies in the bag, suddenly they found themselves being considered genuine title contenders, a near unthinkable prospect not long ago.

Wales too have upped their game since the start of the competition but while there was no shock win for Warren Gatland's men they are most certainly on an upward curve.

In their opening encounters against South Africa and Samoa, it was the Welsh defence that impressed while against Namibia and Fiji some razor sharp attacking was on offer.

Key to both side's resurgence has been the presence of an incredibly talented loose trio.

For Ireland, Sean O'Brien, Stephen Ferris and Jamie Heaslip have been colossal with O'Brien one of the form players in world rugby at present. Such has been the impact of Ferris and O'Brien that even with a slightly off-colour Heaslip in the mix, the Irish back-row has dominated all before them.

They face a stiff test against Wales, though, and the outcome of the loose forward battle will be crucial to determining the end result.

The return from injury of flanker Dan Lydiate is a massive boost for Wales. Lydiate gets through an incredible amount of work and opens up the game for skipper Sam Warburton to snaffle possession and for Toby Faletau to go on his barraging runs.

It's not only the back-row where there will be a tight tussle but also up front.

The Irish scrum was on fire against Australia but against Italy they looked a little less impressive, at least while Martin Castrogiovanni was on the park.

Conversely, the Welsh scrum has gone about their business quietly, not attracting too much attention but that's certainly not because they can't. With Gethin Jenkins in particular looking sharp, the scrums and set-pieces in general will be an interesting contest.

Irish hooker Rory Best's struggle with injury in the lead up to the contest has been well documented and the Welsh will look to put Best under pressure early to test just how fit he is.

One imagines that the game will be won and lost in the forwards, with both back-lines capable of turning on the magic if given good, quick front-foot ball.

Indeed, it's amongst the backs that the most interesting selections have been made.

Gatland has stuck with Rhys Priestland at fly-half and the Scarlets man deserves the nod over the more experienced Stephen Jones. James Hook too may have got a look in at ten but instead finds himself on the bench. It may be due to a lack of fitness but for all his versatility, Hook cannot find a place in the starting XV, with Leigh Halfpenny preferred at fifteen.

Like Gatland, Kidney faced a difficult call at ten and while Gatland went with youth, Kidney has taken the alternate route and retained Ronan O'Gara at pivot.

O'Gara has been forced to sit in the shadow of Jonathan Sexton in recent times, with the Leinster man Kidney's preferred option for the opening stages of both the Six Nations and the World Cup.

The 34-year-old O'Gara's kicking is likely to be the factor that swung matters in his direction. Superior from the kicking tee and out of hand, O'Gara will look to kick for the corners initially and keep Wales on the back foot before Sexton likely enters the fray at a later stage with some additional flair.

When the two teams met in the Six Nations earlier in the year a bruising battle ensued that should only be magnified on the game's greatest stage. It's going to be cut and thrust stuff with neither side giving an inch against opposition that they know well.

Ones to watch:

For Ireland: It was always going to be a close call as to which of Jonathan Sexton or Ronan O'Gara won the battle for the number ten jersey. O'Gara has seen off the challenge of his younger team-mate and Declan Kidney will need the Munster fly-half to repay the faith shown in him.

For Wales: George North was billed as one of the potential stars of the tournament in the build-up and the big winger hasn't disappointed. Up against Keith Earls who has flattered to deceive of late, North could prove a real handful for the Irish defence.

Head to head One can't overstate just how big the battle between the loose forwards will be. It's mouth-watering stuff especially for the neutral. Relentless on attack and defence, the Irish may just have the edge but boy will they be made to work had for every inch!

Recent results:

2011: Wales won 19-13 in Cardiff
2010: Ireland won 27-12 in Dublin
2009: Ireland won 17-15 in Cardiff
2008: Wales won 16-12 in Dublin
2007: Ireland won 19-9 in Cardiff

Prediction: It could go either way and it's sure to be a tight, titanic battle. However, overall Ireland just have the edge and will take the game by five!

The teams:

Ireland: 15 Robert Kearney, 14 Tommy Bowe, 13 Brian O'Driscoll (capt), 12 Gordon D'Arcy, 11 Keith Earls, 10 Ronan O'Gara, 9 Conor Murray, 8 Jamie Heaslip, 7 Sean O'Brien, 6 Stephen Ferris, 5 Paul O'Connell, 4 Donncha O'Callaghan, 3 Mike Ross, 2 Rory Best, 1 Cian Healy.
Replacements: 16 Sean Cronin, 17 Tom Court, 18 Donnacha Ryan, 19 Denis Leamy, 20 Eoin Reddan, 21 Jonathan Sexton, 22 Andrew Trimble.

Wales: 15 Leigh Halfpenny, 14 George North, 13 Jonathan Davies, 12 Jamie Roberts, 11 Shane Williams, 10 Rhys Priestland, 9 Mike Phillips, 8 Toby Faletau, 7 Sam Warburton (c), 6 Dan Lydiate, 5 Alun-Wyn Jones, 4 Luke Charteris, 3 Adam Jones, 2 Huw Bennett, 1 Gethin Jenkins.
Replacements: 16 Lloyd Burns, 17 Paul James, 18 Bradley Davies, 19 Ryan Jones, 20 Lloyd Williams, 21 James Hook, 22 Scott Williams.

Date: Saturday, October 8
Kick-off: 18:00 (05:00 GMT)
Venue: Wellington Regional Stadium
Weather: Showers earlier, clearing later Max 12°C Min 7°CReferee: Craig Joubert
Assistant referees: Wayne Barnes, Romain Poite
Television match official: Giulio De Santis
Assessor: Bob Francis

By Julia Harris