Ospreys v Leinster (Sunday, 4.0, LIVE RTE2) - This is about as big a hoodoo hovering over the heads of Leinster as there is in Europe. Clermont-Auvergne even come second to The Ospreys when it comes to recent head-to-heads.
The Ospreys cut down Leinster home and away in the PRO12 League last season before applying the 'coup de grace' in a magnificent final in Shane Williams' fairytale farewell at The RDS in May.
This has been the single most damaging Welsh opponent to Irish rule of this competition. The Ospreys are out in front as the four-time winners of this competition.
In fact, Ulster are the only Irish province to have won in Swansea -- it came about last September -- from the last eight Irish raids on The Liberty.
The removal of Ireland-qualified tight-head Michael Bent from the equation -- the six-day turnaround to Ireland-South Africa is not sufficient recovery time -- further weakens Leinster where Ospreys are strong.
Coach Joe Schmidt will have to orchestrate something of a surprise given the number of Ireland internationals unavailable and a cluster of injuries.
You would have to think that centre Eoin O'Malley (pictured) and flanker Rhys Ruddock are two of a number of contributors short on match sharpness.
It remains to be seen how the three-quarter line will operate without the reassuring presence of Isa Nacewa. It will all start in the pack where the set-piece and breakdown will be critical.
Leinster may have won their last four matches in Europe and the PRO12, but they have not been able to get the better of The Ospreys away since September 2009.
The Welsh club has won four of the last five clashes between these powerhouse clubs and Leinster have lost two of their last three away dates in the League.
Verdict: The Ospreys