This is knockout rugby. There is no tomorrow for either of them. The spectre of Munster means Leinster cannot afford the luxury of contemplating a first home final against the Ospreys in the newly formatted Magners League.
It simply won't do for Michael Cheika's players to take either eye off the ball. Munster are past masters at defying logic and reason. There is nothing to get the adrenaline flowing down south quite like the tag of underdogs and the sight of a blue jersey.
Indeed, the Ospreys' match winner James Hook echoed the attitude of his team-mates in the aftermath of their 20-5 semi-final handling of Glasgow Warriors at The Liberty Stadium last night. "We just want Munster to do us a favour now," said Hook, in relation to the hometown appointment the Ospreys would gain as overall second seeds against fourth seeded Munster in the final.
The problem for them is that there are still a few old soldiers around who were there when Leinster looked beyond Perpignan in the 2003 Heineken Cup semi-final to a juicy home date in the final. Brian O'Driscoll, Gordon D'Arcy and Malcolm O'Kelly paid the price for that slip.
It has informed their approach to big-time rugby ever since. The telepathic O'Driscoll and D'Arcy are too long at this level and coach Cheika too dedicated to leaving the province as a winner for complacency to become a factor.
If Leinster take one glance away from what is their total focus -- to make it four consecutive wins over Munster -- they will be dumped on their rears in the same way the Blues stunned Munster in last year's Heineken semi-final.
OK, Paul O'Connell lost his battle to beat a troublesome groin injury to land a monumental blow to Munster's plan to find sweet consolation for being second best this season.
Lock Mick O'Driscoll is many critics idea of Ireland's third best second row and he will maintain Munster's options at the lineout in an intriguing individual set-to with O'Kelly.
There was a glint in the eye of the retiring O'Kelly this week. This is his shot in the last chance, or second-last chance, saloon. It is in his nature to make the most of this opportunity.
Leinster will also have to do without their captain Leo Cullen. He is a clever game manager with a true sense of leadership. This slack will have to be taken up by interim armband holder Shane Jennings.
It is difficult to understand the reasoning behind Tony McGahan's decision to leave hooker Jerry Flannery and openside David Wallace on the bench. It is also a shame that the after-shock of Leinster and Munster's exit from the Heineken Cup has hindered the build-up to the Magners League semi-final.
There was far greater hype and hysteria over the regular season meetings between Ireland's pair of tyros than there has been for the match that means most in the overall scheme of things.
Leinster: R Kearney; S Horgan, B O'Driscoll, G D'Arcy, I Nacewa; J Sexton, E Reddan; C Healy, J Fogarty, S Wright, N Hines, M O'Kelly, K McLaughlin, S Jennings (capt), J Heaslip.
Munster: P Warwick; D Howlett, K Earls, J de Villiers, L Mafi; R O'Gara (capt), T O'Leary; M Horan, D Varley, J Hayes; D O'Callaghan, M O'Driscoll; A Quinlan, N Ronan, N Williams.