ALL eyes are on the Millennium Stadium for round four of the Six Nations, unless you've got John Inverdale's red rose-tinted spectacles on.

The importance of the Calcutta Cup fixture at Twickenham is dictated by events in Cardiff; a Welsh win means it's a three-way title tilt whereas Irish joy leaves them an Edinburgh success away from a Grand Slam.

It's a game with the feel of an autumn international against one of the southern hemisphere big guns. It will be tense and tight rather than open and expansive but that doesn't quell the excitement.

When South Africa and New Zealand went toe-to-toe for the Rugby Championship in 2013 they produced an absolute thriller featuring nine tries and some scintillating rugby.

This afternoon's fare won't rival that classic encounter in terms of a highlights reel – there have been just 13 scores in the six Tests featuring the sides in the tournament – but it is a game that will be full of tactical intrigue as well huge collisions.

The battle of the brain is every bit as important as the battle of the gain line. The ability to act with clarity amid all the mayhem and when limbs are tired, something that Irish talisman Paul O'Connell is a master of, will be vital.

"It's going to be an arm-wrestle for 80 minutes, and that is what we've prepared for," said Wales forwards coach Robin McBryde.

"They play a big pressure game, and if we can react positively to that and stay in the fight, that will give us a good chance of winning.

"There is a lot of stake. Ireland are on course for a Grand Slam, and just to get away from Cardiff with a win, that's all they will be looking to do. With regards to playing any attractive rugby, that will come second."

Few Welsh supporters will be complaining if their side manage a rather ugly repeat of the 2011 win when the only try was Mike Phillips' effort from an illegal quick lineout.

As entertaining as the 2013 encounter between the sides was, it wasn't much fun to see Irish celebrations after repelling a second half comeback for a 30-22 success.

Ireland head to the Millennium Stadium with a stingy average of nine points conceded per game under Joe Schmidt in the Six Nations and France lock Romain Taofifenua is the only man to have crossed their line this year.

Given that Warren Gatland's pre-tournament pledge to hold plenty back for the World Cup it will be a surprise if Wales change from their usual blueprint in order to try and battle their way past the resilient Irish.

The visitors, no doubt aided by Gaelic football, are notoriously strong in the air but the hosts back themselves in that department with Dan Biggar and Jamie Roberts as useful under the high ball as the back three of Liam Williams, George North and Leigh Halfpenny.

Wales will attempt to muscle their way over the gain line – failure to do so was catastrophic against the English – and will play the pressure game to earn Halfpenny shots at the sticks.

They stood up to Les Bleus at the set piece but face a sterner challenge than the ramshackle and dunderheaded French with O'Connell set to put heat on hooker Scott Baldwin, a top performer in Paris but hardly the most secure of lineout operators.

And then there's the breakdown where the common consensus is that Ireland get away with murder in terms of entry and supporting their body weight. Hopefully referee Wayne Barnes, a replacement for Steve Walsh, won't be talk of the post-match press conferences.

Ireland are third in the world rankings and on a streak of 10 Test wins so it will take a huge effort to derail their charge to the title; Wales must produce their best display since the heartbreaking loss to South Africa in Nelspruit.

It all points to a close contest and fingers crossed Wales will be heading to Rome with a chance, albeit slim, of lifting the Six Nations trophy.

Wales: L Halfpenny (Toulon), G North (Northampton), J Davies (Clermont Auvergne), J Roberts (Racing Metro), L Williams (Scarlets), D Biggar, R Webb (both Ospreys), G Jenkins (Cardiff Blues), S Baldwin (Ospreys), S Lee (Scarlets), L Charteris (Racing Metro), A W Jones, D Lydiate (both Ospreys), S Warburton (captain, Cardiff Blues), T Faletau (Newport Gwent Dragons).

Replacements: R Hibbard (Gloucester), R Evans (Scarlets), A Jarvis (Ospreys), J Ball (Scarlets), J Tipuric (Ospreys), M Phillips (Racing Metro), R Priestland, S Williams (both Scarlets).

Ireland: R Kearney (Leinster), T Bowe, J Payne (both Ulster), R Henshaw (Connacht), S Zebo (Munster), J Sexton (Racing Metro), C Murray (Munster), J McGrath (Leinster), R Best (Ulster), M Ross, D Toner (both Leinster), P O'Connell (captain), P O'Mahony (both Munster), S O'Brien, J Heaslip (both Leinster).

Replacements S Cronin, C Healy, M Moore (all Leinster), I Henderson (Ulster), J Murphy, E Reddan, I Madigan (all Leinster), F Jones (Munster).

Referee: Wayne Barnes (England)