As Leo Cullen trudged to the sin-bin for his deliberate knock-on with just under 15 minutes gone on Friday night, the Thomond Park crowd settled into a hush so that Ronan O'Gara could go through his penalty routine. Just at that moment, whoever was running the outside broadcast in Setanta Sports took their life in their hands and handed over to Matt Williams who was standing on a scaffold just between the terrace and the top tier of the West Stand.

Or, more accurately, they took Matt Williams's life in their hands because no sooner had silence descended all around the ground than out into the Limerick night rang the familiar Noo Saaath Waayyulles drawl of the former Leinster, Ulster and Scotland coach, lauding the intensity and physicality of the opening exchanges. He got about half a sentence in before he was angrily shouted down.

You had to feel for Williams. It wasn't that he didn't know the traditions of the place – and it's fair to say that the gleeful barracking of Jonny Sexton throughout the night from sections of the Thomond crowd was altogether worse – just that he'd been handed a live grenade and couldn't very well stick it in his pocket for a few seconds while everyone took a time-out. It wasn't a time-out kind of night.

Both teams took plenty home with them for the week ahead. Leinster got on the road back to Dublin happy to have detoxed after last weekend's indulgences against Connacht. Word had it they spent the early part of the week doing some fairly hefty chain-gang time for their sins and they looked a different side on Friday night. More purposeful, more dogged, more up for dirtying their hands. When Michael Cheika leaves for Paris in a couple of months, he can reflect happily on being around for that change in culture at least.

"It's not that I was angry last week," he said afterwards (referring to the aftermath in the RDS when, reader, we can confirm that he was at the very least a little bit cross). "It's more that in the past, we might have let something like that slide and gone, 'Well, you know, we won without playing very well so that's great.' It's important not to let your standards slip. Sometimes it does happen and you've got to react to it.

"All we concentrated on was to get right this week those things we got wrong last week. For me, it was the way we reacted from last week that was predominantly pleasing. To make sure we got those technical areas of our games right and to make sure the physical battle wasn't given away."

Cheika was actually in Paris yesterday to run a final rule over Clermont Auvergne as they played his future employers Stade Francais. If last weekend's dawdling performance at the RDS wrote his team talk for him before Friday night, there's a fair chance that the follow-up to October's 30-0 Magners League win over Munster – a lifeless 9-12 home defeat to London Irish – will get a mention between now and Friday night.

"We won't know until next week if there's any difference between this time and last time," Cheika said. "But the experience of what happened last year has already been spoken about and if you don't learn from experience, you're not very clever. We're going to be playing what I think we can consider the best team in Europe at the moment. They've been performing at such a high level that – and this is not just talk – we're going to have to play better than we did against Munster."

As for Munster, there is plenty to fret over ahead of Saturday's quarter-final at home to Northampton. For one thing, Friday night was a wrenched tight game of the kind they generally find a way to squeeze a win out of when they're on song. But at times near the end, they looked a little shapeless and, worse, leaderless. Save for the indefatigable Alan Quinlan – you'd be hard pushed to find a player on either side who enjoyed the nip and niggle of the evening more than he did and he was chugging forward right until the end – they finished the game with more Indians than chiefs.

And it told. Donncha O'Callaghan spoke afterwards of not getting "within an ass's roar of being close enough to let Rog have a pop at a drop goal". Munster just couldn't put the phases together with enough patience to get within striking distance, too often leaving a runner isolated as they went on the hunt for the big play rather than the percentage one. It was crying out for Paul O'Connell to direct the operations.

That isn't why the game was lost; just why it wasn't won in that final five minutes. No, why it was lost against Leinster was that Cheika's side were better in most facets and broke even in just about them all. Afterwards, all Munster players and coaches pinpointed lapses in discipline.

"They played such a smart game," said O'Callaghan. "Penalties and discipline killed us. Discipline's an individual thing. I was at fault and so were others. The penalty count was 15-9 or something so that speaks for itself. Taking nothing away from them, they were outstanding."

Tony McGahan, while generally talking up the positives for Munster – good defence, strong tackling, decent in the setpiece where Leinster had killed them during the 30-0 match – was in full agreement with his second row when it came to discipline.

"I thought some of the stuff we did there was crazy at times," he said. "We really need to trust our defence and trust what we're trying to do there. But when players go on their own and play for themselves when they're clearly not in a good position to make that decision, that's going to cost you. It cost us six points this evening and small margins are going to matter in big games."

In that final quarter, one player who was clearly a bit mystified to be sitting on the bench was Jerry Flannery. Despite surely needing game-time after his six-week suspension, he was called ashore with just under 20 minutes to go. As he left the field, Sexton kicked what turned out to be the final score of the evening to put Leinster 16-15 ahead, and Flannery was very obviously annoyed at having to make way. "I would really have liked to play the whole game," he said. "But the guys on the line made a call and I came off. I've just got to suck it up now and put this on my shoulder and carry it for the next week."

No better man, you'd have thought. And, by all measures of history, no better men than he and his brethren to turn it around. Still, the win in Perpignan aside, the majesty has been lacking this season. Leinster on Friday night was a chance to claw some of it back and it was missed.

"It is a setback, definitely," said Flannery. "Generally in the last few years, we've managed to pull out a good league win heading into the last few games of the Heineken Cup as a sort of a set-up for us. That's not happening this time. You could pick out discipline but I think Leinster just played smarter than us. But you have to get past it now and find the positives. That was a big effort we put in there tonight and it should stand to us. We could have played a far less intense league game and be going into next week needing to step it up."

You suspect Munster will find a way, if for no other reason than they generally do. But it's a leap of faith. Not the first, not the last, just the latest. How many more can they make?

mclerkin@tribune.ie