Leinster v Munster
The Aviva Stadium, tonight (ko 7.0) live RTé 2
This must be the best attended curtain-raiser in the history of club rugby.
Leinster and Munster will go about putting the building blocks in place for their Heineken Cup quarter-finals away to Toulon and at home to Toulouse, respectively, at a sold-out Aviva Stadium.
"It's sudden death. You lose; you're done. That gives you pretty good clarity going into knockout rugby," said coach Matt O'Connor.
"This week's important to reintroduce the starting Test guys. They've trained very well. They are re-acquainted with our environment, our systems and our structures. We'll be certainly better for the hit out."
O'Connor's men have been good, not great, this season. There are many reasons for that, changes in systems, a revolving door of a rotation policy forced by the international recruits.
The coach has also had to deal with what he had to at Leicester Tigers in the Premiership. Clubs come to defend and frustrate at the RDS in the same way they do at Welford Road.
"We will be looking to play. They'll be trying to stop us playing. It will come down to, who does that the best will probably get the result," said O'Connor.
"Have we been all-singing, all-dancing, as good as we would have liked to be? No. But, you have to factor into that some of the psychology of the opposition.
"It is a huge focus of the opposition to stop us playing. From that end, it makes it very difficult to get that sort of continuity across the course of 80 minutes."
Leinster have shown what they can do, strangely, away to Northampton Saints and Castres Olympique in the Heineken Cup. O'Connor is not quite able to bring himself to admit to a level of frustration that the Northampton blow out has been the exception to the rule.
"That certainly was our peak performance throughout the year without question," he said.
"But, I think, relative to the combination, relative to the blokes we have and haven't had, it's about winning. There have been glimpses. Have we put out an 80-minute performance? Probably not.
"If you took out the first 15 minutes in Castres, we were pretty good to come from behind 14 down and to win in that game was a pretty pleasing performance. The Ospreys was a really good result. Very few teams win there."
Munster are just the type of animal to trigger a response in keeping with Leinster's position as PRO12 League leaders and it has taken a large squad, not just the first XV to put them on top.
"Different bodies; different stakes," said O'Connor, in reference to how Leinster have kept winning without the bulk of their first team during the international windows.
"But, you know, the Dragons win in November was enormous for us and the away win at Zebre with so many blokes missing put us on that roll of momentum that was really important as well."
The danger around Leinster's hard-working victories is that a day is coming when they will suddenly click into gear, find their rhythm and precision to rack up points very quickly.
The energy and enthusiasm generated through the squad from winning, added to the return of the frontline Ireland internationals, could just make for a lethal cocktail.
"I think that gives me and the group a lot of confidence that we are building to a really special performance," he said.
"Hopefully, fingers-crossed, Saturday and Sunday week and in those massive games to come at the back end of the season, we are in a good place and building nicely."
The simple truth is that Leinster's season is building towards Sunday week and how they will counter the multiple threats of Heineken Cup champions Toulon.
It all starts this evening: "We've sat down as a coaching group and we've looked at Toulon and some of the things we want to do. Some of the things are a bit different," he said.
"Some of them can grow out of what happens on Saturday night so we will have to wait and see what develops out on Saturday relative to the strengths Toulon have, and they have plenty of them."
Leinster: R Kearney; F McFadden, B O'Driscoll, G D'Arcy, L Fitzgerald; I Madigan, E Reddan; M Bent, R Strauss, M Ross, D Toner, M McCarthy, K McLaughlin, S Jennings, J Heaslip (capt).
MUNSTER: F Jones; K Earls, C Laulala, D Hurley, S Zebo; I Keatley, C Murray; D Kilcoyne, D Varley, BJ Botha; D Foley, P O'Connell; P O'Mahony (Capt), T O'Donnell, J Coughlan.