Leinster's Jonathan Sexton and Eoin Reddan will have to play out of their skins to force Declan Kidney's hand ahead of Ireland's tussle with England at Twickenham next Saturday.
The malfunction of Ireland's half-backs Ronan O'Gara and Tomas O'Leary in Paris reopened the debate over who is best equipped to take Ireland forward to the 2011 Rugby World Cup.
While this central issue will not be decided by how Sexton and Reddan fare against the Scarlets in the Magners League at the RDS this evening (6.30), the Leinster duo could just do enough to convince Kidney they are worth a shot at starting in Twickenham.
Coach Michael Cheika, a man known for planning ahead, took time out to emphasise the residual memory that still rankles him from Llanelli's stunning 52-23 Magners League shock at the RDS in October 2007.
"We are still haunted by that game when they came up here and gave us a tonking a few years ago," said Cheika. "But every step now is a step closer to the top four.
"It is good to be at home too because we haven't played together for a while."
The Scarlets have been able to call on Wales's current Six Nations internationals -- scrum-half Martin Roberts, centre Jonathan Davies and hooker Ken Owens -- to strengthen their case for completing the double over Leinster.
They will provide extra quality to a 15 already sprinkled with class.
Obviously, it is the well balanced centre partnership between Regan King and Jonathan Davies that will command much of Leinster's attention. The power of Davies and the beautifully astute playmaking of King can carve up the best defences in the game.
"That's something to be excited about. It should be quite intriguing to see," said coach Nigel Davies. "Leinster are a strong squad, even without a number of their internationals -- and that's what you need to be successful," he said.
Australian Lyons added: "We were very disappointed with the Heineken Cup results against Leinster. We have to improve on those performances."
It will be up to Leinster to remind the Scarlets that the back-to-back double for the European champions in the Heineken Cup is a true reflection of the difference between these two clubs.
Leinster: G Dempsey; S Horgan, F McFadden, S Berne, I Nacewa; J Sexton, E Reddan; S Wright, B Jackman, CJ van der Linde, M O'Kelly, D Toner, K McLaughlin, S Jennings (capt), S O'Brien.
The Scarlets: D Newton; D Evans, R King, J Davies A Fenby; R Priestland, M Roberts; I Thomas, K Owens, D Manu, D Day, D Welch, R McCusker, J Edwards, D Lyons (capt).
LEINSTER v SCARLETS LIVE SETANTA 1 (KO 6.30)