The starting point for today’s fascinating Six Nations contest has to be the coaching box. Two polar opposite coaching geniuses with entirely different, but equally effective, approaches come head to head once again in their last Six Nations roles for their adopted countries.

Gatland stands on the brink of unprecedented achievement in leading Wales to a third Grand Slam on his watch. Ireland have only achieved three in our entire rugby playing history. Yet, for some strange reason, he still struggles to get the recognition he deserves. He will be bulling for a win.

Opposite him, a man who has had a transformative effect on the game in this country. Schmidt equally craves a win today, not for any personal gratification but because it would sign off a difficult and challenging campaign on a very positive note before re-assembling later in the year for a final push at World Cup glory.

Given the current state of Welsh regional rugby, with no side in the knockout phase of the Champions Cup and making little impact in the Guinness Pro14, winning this championship amidst “Project Reset” or “Project Inept” (as the WRU’s attempts at revamping the regional game was recently described by the Ospreys board), would be some achievement by Gatland.

All that will be parked today as two dogged and highly motivated Kiwis seek to outsmart each other. Schmidt’s achievement in getting Ireland back on track mid-tournament, after the disappointment of that opening day collapse to England, is noteworthy but the impressive win over an inept French side needs to be backed up with another victory today or, at the very least, a quality performance.

Wales are chasing a 14th consecutive win and are notoriously difficult to beat in the highly charged atmosphere that accompanies all the big games at the Principality Stadium. Gatland knows his side will be forced to play without the ball for long periods today and has prepared accordingly. Schmidt, on the other hand, will have to engineer more than just innovative power plays off lineouts to break down the best defence in the tournament. So how do they go about it?

2. Breakdown efficiency

While the battle at the breakdown is a key element of every game, an inability to compete on equal terms here with Wales will prove fatal. It has become one of the key tenets of their game to the extent that, in common with Australia playing David Pocock and Micheal Hooper together, Wales also look to play two fetchers in their back row.

Gatland has tinkered with this for some time, initially only pairing former Lions captain Sam Warburton and Justin Tipuric together against certain opposition but has expanded it further since Warburton’s premature retirement. Cardiff’s Josh Navidi emerged as a real talent when Wales had a back row injury crisis last year and has been outstanding in this championship in tandem with the under-appreciated Tipuric.

Wales look to achieve a 70% ruck competition. By that Gatland means that he expects to see a contest for a turnover by a jackaler in seven out of every 10 tackle situations. At worst that contest for possession will slow down the recycle of the ball, buying precious seconds for the defensive line to set. Even better if it results in a turnover or penalty against the tackled player for not releasing.

In Navidi, Tipuric, hooker Ken Owens and captain Alun Wyn Jones, he has four outstanding exponents of the art. Wales boast a highly impressive defence structure and, at times, are more effective without the ball than with it. Against Scotland they made 194 tackles in the second half alone when the hosts dominated possession. They are comfortable defending.

If Ireland are going to stress that well-oiled defence, then they need to outpoach the poachers. That is why the introduction of Tadhg Beirne to the second row for the unfortunate Iain Henderson could prove a blessing in disguise. Beirne is a master of the art, the leading exponent in the Champions Cup this season to date on 13. He has waited for this opportunity for a long time and will relish going head to head with so many of his former Scarlets teammates.

His presence along with the return to arms of Sean O’Brien, who will be champing at the bit having been omitted for the French game, working in tandem with Peter O’Mahony and Rory Best who are both proficient in contesting for turnovers could prove crucial in shaping the direction of this contest. It also brings a strong balance to the pack, enabling Cian Healy, Tadhg Furlong, James Ryan and CJ Stander major on making trademark, explosive, carries.

3. Wigan’s defensive Warriors

When you examine the makeup of the Welsh team it’s difficult to fathom that they’ve won 13 tests on the trot. Two excellent second-half performances against France and England apart, they have looked distinctly ordinary at times in this tournament.

The fact that they are on the cusp of a 12th Grand Slam in their history is very much down to the fact that their most experienced and influential players in British and Irish Lions Ken Owens, Alun Wyn Jones, Tipuric, Jonathan Davies, George North and Liam Williams are in top form and inspiring all those around them.

That said, their lineout is particularly vulnerable - statistically the worst in the championship - their attacking game is stuttering with nine tries in the four games to date while the place kicking of Gareth Anscombe is also suspect. He is under big pressure to perform given Dan Bigger’s presence on the bench.

What Wales do have is a massive workrate, especially in defence; they are incredibly resilient and have a very good kicking game which led to a number of their tries in the earlier rounds. The back three, and Williams in particular, are superb in the air and more than capable of dealing with Ireland’s much-heralded kicking game. They are a clever side and Schmidt has to come up with a plan to outsmart them.

But despite their excellent run of form, they are very beatable. Scotland dominated for long periods against them last time out but injury robbed them of their scoring power in the back three. In Jacob Stockdale and Keith Earls, Ireland have that in abundance.

This one could well come down to sheer grit and staying power. Earlier in the week forwards coach Robbie McBride said: “I think Ireland were a bit shocked by the physicality of England in that first game.”

You can be sure that Gatland will challenge his players with reproducing the same level of physicality England brought to Dublin. Ireland need to be ready for that and to win the big collisions.

There’s every chance the outcome will come down to the side that defends better and in that the influence exerted in the respective camps during the buildup by former Wigan Warriors teammates and league greats Andy Farrell and Shaun Edwards could prove the difference.

There is nothing separating these two sides but raucous home support does offer Wales a slight edge. At their best, Ireland are capable of dealing with that but need to deliver the clinical efficiency and error-free rugby that accounted for New Zealand last November if they want to spoil the latest Welsh Grand Slam party. It is something they are more than capable of achieving.