It was an evening sprinkled with delicious irony. Munster's raging passion denied Leinster a maiden Celtic League/ Heineken Cup double, violently upsetting those who had already seen fit to shower some of Alan Quinlan's mother's holy water upon the grave of this redoubtable team.
"It's a good thing to be in a bit of a down place and win the Magners League," noted Paul O'Connell, before lifting one of only two trophies available to his side this season. "We'll take heart from this, take mental strength from this."
Leinster's brave efforts were dripping in a cruel irony too; they didn't have 80 minutes of intensive rugby in them, but, had they been clinical enough in the dazzling moments when they did reach their Cardiff heights, the booty may have been theirs.
Mentally, and physically, it was just impossible, whether it was the waning energy in the bodies of Sean O'Brien and Richardt Strauss, or the penalty decisions on three separate occasions when Leinster took the wrong option.
"We just lacked that bit of sharpness, that bit of edge," said Leo Cullen, for whom life gets even more hectic next week when he walks down the aisle.
"It was disappointing that we made some silly decisions. We had penalties and turnovers, but we just started forcing things. It was like we were playing into their hands.
"We just lacked a bit of calm. I don't know if that's a result of fatigue. When you're fatigued you make silly decisions."
Paradoxes abounded. Few could have predicted a 3-0 try count in Munster's favour, particularly after some 497 minutes of impotence covering some two years of this fixture; that Leinster were denied a try was an equally stunning effort.
And if the defence, perhaps, earned the ultimate praise, beyond the revived feral elements that drove Munster on their sacred turf, the scrum applied the defining hammer blow.
Incongruity continued to flow as freely as the celebratory cider in the game's aftermath, too.
John Hayes, whose reticence when confronted by the media makes Bob Dylan seem like an outgoing sort of chap, is wandering around the Thomond Park tunnel with a mischievous grin on his face.
"Any chance of a word Bull?" is the cry. "Arra, why not!" he replies. Such is the historic nature of the occasion, we beseech No 8 James Coughlan to capture the moment on film.
An hour or so earlier, Hayes had emasculated his fresh opponent to such a degree of submission that Nigel Owens felt it necessary to award Munster the penalty try that confirmed their title.
Lasting 80 minutes, approaching the age of 38, was a shock in itself, but being able to make such an impact, within what has often been a pilloried and concertinaing scrum all season, at such a late stage of the game, was seismic and a fitting conclusion to a raucous Irish rugby season.
And an end to Hayes? You must be kidding. Too much work to be done.
"I don't know if it's the end," he says in his first post-match interview since the invention of the dictaphone. "That's the honest answer. I'll just wait and see how it goes.
"I feel fine now, but it's like anything, when you get a win things don't hurt. But it's the end of the season and I'm looking forward to a break now. New Zealand? We'll wait and see."
We believe he's signed up until after October at least; the presumption was that he would be tending to the home fires of Magners League combat while the World Cup was on. Now, the case to bring him back to the country where he learned how to prop appears utterly compelling.
"I've played 80 minutes all my career, so it's nothing new to me, like," demurs the Cappamore man, who only started playing the game as an 18-year-old.
"I've been doing it for years. I haven't done it much this year, maybe, but I have done it every other year. I started late, and I'm not saying that's the right thing for any young fella, but that definitely did help me in terms of development."
The press officer appears and suffers almost instant coronary failure upon seeing rugby's Greta Garbo rapping away to his heart's content.
"Ah go away, I'm only getting warmed up," Hayes cajoles. This is, indeed, a unique evening. A special night to bow out, perhaps? If this were the end?
"It would, yeah," he says quietly. "It was a great match, a great way to finish the season, anyway.
"We've been where Leinster have been before and if you play big matches every week, it does take it's toll.
"They had a huge game last week and there was travel involved, whereas we had two weeks to prepare. It was just a matter of getting the two weeks right, of not going off the boil and keeping that balance right.
"Ah, it's just good to get the win. It's been a long season, obviously it's been disappointing in Europe. We've been good in the Magners, but finishing the league stages on top doesn't get you anything, so it was important to get the knockout wins."
So much of Saturday's theatre may have seemed valedictory, as perhaps Hayes' appearance before us now. But, as he assessed the retirement of another comrade, Alan Quinlan, it was with the future in mind.
"Of course we're going to miss Quinny. He's a huge character. He's been here a long time and it's not just that -- he's a character in the squad, a personality, and it's all those things together that makes him what he is.
"He'll be a big loss, but that's what happens. There are new Quinnys and new fellas starting, and that's the way it is, the whole thing keeps moving on."
Ronan O'Gara's clarion call announced as much. "We've been immersed in negativity it seems all year and it takes a lot of courage to do this," he said. "It's a good day for Munster. We were on the ropes and we showed balls. The future is good."
Not an end, but a beginning.
And for John Hayes? Well, the Bull's fields won't be farmed by themselves.
"I'll go straight home because it's a busy time of the year and I have to get jobs done," he says.
"Straight home and I'll get to do them, if the weather holds anyway. It would want to clear up a small bit!"
And for the first time on this remarkable evening, a frown creases the brow of the Bull Hayes. Denis Leamy didn't need to remind us, but he did. "That man is a legend."