Luke Charteris, in the scrum cap, stops Cian Healy en route to setting a new Six Nations tackles record © Getty Images

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Sometimes people do go to see rugby to see great defence. The guts of this gripping contest were to be found in an extraordinary seven-minute passage in the second half, with Wales leading 15-9.

Ireland attacked and attacked, endlessly probing and recycling, keeping the ball through countless phases. Wales tackled and tackled, meeting every Irish thrust, and gave away only a single penalty during the entire period. You could isolate individual moments - Dan Biggar's momentum-crushing hit on Rob Kearney, Jamie Roberts halting the tricky Robbie Henshaw, Roberts again on Tommy Bowe and George North foiling the Ulsterman for a second time in as many minutes - but these were peaks amid a quite remarkable passage of sustained high-tempo intensity.

The two matched each other for discipline, control and sheer unrelenting physical commitment. It had echoes of another extraordinary passage more than a decade ago in a Heineken Cup final at Twickenham, when Toulouse produced one of those bursts of high-octane improvisational brilliance in which they resembled nothing more than a great jazz band, and Wasps matched them at every turn. And Wasps were also eventual winners.

Common to both, of course, was the architect of both defences - Shaun Edwards. Television pictures showed his fury and disbelief when Liam Williams was adjudged to have given away that single penalty, and his delight when a hard-won turnover finally lifted the siege.

The acclaim from the crowd when that happened was worthy of a winning try - and with good reason. There were other crucial moments in a superb contest, a slow-burner which caught light after half-time and rarely slackened thereafter, but this was the point at which the game was won and lost. Not least, it was also the moment at which the crowd and its mounting excitement became a factor in the contest.

It was no coincidence that Wales' decisive score came soon after. There were both a turnover and a stolen line-out in the period of play which built up to Scott Williams, fresh, incisive and a proven scorer of important tries, darting through a gap to the Irish line to give them a 20-9 lead.

It was the second time Williams had threatened in the two minutes since replacing Roberts, an inspired change which added a little extra invention and attacking edge after Roberts had given his all in a heroic defensive stint which featured a head-to-head collision with Irish hooker Rory Best.

Ireland were worthy champions last season and by far the best performer so far this, and did not readily give up on their hopes of a Triple Crown and Grand Slam, pressing again for much of the final quarter. There was little doubt about the penalty try which Wayne Barnes awarded with 11 minutes to go.

But Wales were able to live on the credit they had built up in dominating the first 15 minutes and their subsequent defensive effort and close out their best victory since England were beaten here two seasons ago. They had played with fire, control and discipline from the start - denying Ireland the turnovers they took from England in the opening stages two weeks ago and instead turning their possession into points as Leigh Halfpenny landed four penalties in the first 13 minutes.

There was a slightly 'phony war' period to that opening. There often is until the first try is scored, and neither side seriously threatened to do that in a first half that was largely played between the two 22-metre lines. But those early points gave Wales a lead they never lost and a cushion which was ultimately to sustain them through their long periods under intense pressure in the second half.

And there were hints from early on that this might not be Ireland's day, as their usual precision deserted them. Johnny Sexton missed a 35-metre penalty he would expect to land nine times out of 10 in the 14th minute. A blown line-out after they went for the corner rather than points from a 22nd-minute penalty was the sort of mishap we associate with Wales rather than Ireland, and one of four they lost on their own put-in.

Four times in all Paul O'Connell, accorded a rousing ovation by both sets of fans when he ran out alone for his 100th Irish cap, chose to take kickable penalties to the corner. One produced the penalty try, but the other three were fallow - one, in the final minutes as Ireland pressed for the draw which would still have kept them as clear frontrunners for the championship, following that true collectors item, a fumble by O'Connell himself.

On other days, given the possession and position they enjoyed, Ireland might have won with something to spare. They did not play badly, but Wales did not allow them to play terribly well. A key difference from the England game was the Welsh ascendancy at the breakdown, winning seven turnovers to one. Wales also had the edge in the air, where Halfpenny and Dan Biggar did their now standard impersonations of the 'Daring Young Men on the Flying Trapeze' and managed somehow to minimise the impact of Ireland's clear ascendancy in the scrums following Samson Lee's early departure.

And sometimes statistics do not lie. An extraordinary Welsh defensive effort produced remarkable numbers - a total of 289 tackles, shattering the previous Six Nations record of 245 produced by Italy, also against Ireland, last year. Luke Charteris achieved a barely credible 37 tackles, with man of the match Sam Warburton also beating Serge Betsen's previous Six Nations mark of 27.

As the inimitable Edwards often tells us, defence wins matches. And just occasionally it is as inspiring as any victory built on attacking play.

Scott Williams bursts through to score Wales' try - just moments after a heroic goalline stand by the Welsh defence © Getty Images

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