Blues primed to maintain their surge for fourth title
Champions Cup: Leinster v Scarlets (Aviva, Today, 3.30, Sky Sports)
This will all come down to who has improved most, learned most and changed most from the PRO14 League semi-final last season.
From Leo Cullen's point of view, there are no less than ten changes to his starting line-up, some for the better, some not so.
Centres Robie Henshaw and Garry Ringrose, wing Isa Nacewa, out-half Jonathan Sexton and tight-head Tadhg Furlong are carried over as five key figures. In other words, there is just one forward remaining from that day with Cian Healy, Devin Toner, James Ryan, Scott Fardy and Dan Leavy giving the pack a more explosive, more athletic appearance.
"It's hugely important," said coach Leo Cullen, about the front eight.
"The set-piece battle is key to these big games and the teams that do the basics well.
"It's about making sure we provide a good platform and we control possession as well in the right areas of the field and in the right manner.
"The pack is going to play a huge role in the game."
Okay, the loss of Luke McGrath, confirmed this week, the stagnation in Adam Byrne's season, Josh van der Flier's injury and Seán O'Brien's shoulder procedure have been softened by Robbie Henshaw's recovery and Jack Conan's late charge to make the bench.
However, Jordi Murphy is one of the most under-rated loose forwards in Irish rugby as an all-purpose player, with a sound lineout, ground and carrying game.
It is from the pack that Leinster will look to drive a lorry load of carriers through the heart of the Scarlets.
There is no better way around the Welsh club than to go straight through it.
The Scarlets have lost Jonathan Davies and Johnny McNicholl to injury and Liam Williams to Saracens as they retain ten of last year's line-up at the RDS.
Their backs thrive on the Scarlets system rather than individual impact.
They follow that old rugby adage in letting the ball do the work until it ends up in the hands of Steff Evans.
There is tactical interest around why Wayne Pivac has opted for Dan Jones, a fine out-half, Rhys Patchell at full-back, Leigh Halfpenny on the wing. There is also the six forwards-two backs split on the bench with the presence of Will Boyde yet another indicator of how Scarlets will live or die by the breakdown.
Leinster: R Kearney; F McFadden, G Ringrose, R Henshaw, I Nacewa (capt); J Sexton, J Gibson-Park; C Healy, S Cronin, T Furlong, J Ryan, D Toner, S Fardy, D Leavy, J Murphy. Replacements: J Tracy, J McGrath, A Porter, R Molony, J Conan; N McCarthy, J Carbery, J Larmour.
Scarlets: R Patchell; L Halfpenny, S Williams, H Parkes, S Evans; D Jones, G Davies; R Evans, K Owens (capt), S Lee, T Beirne, D Bulbring, A Shingler, J Davies, J Barclay. Replacements: R Elias, D Evans, W Kruger, L Rawlins, S Cummins; A Davies, S Hughes, W Boyde.