The three-time champions, going in search of an unprecedented three-in-a-row, paid the price for a savage injury list before Christmas.
Munster muscled their way through and around an initially truculent Racing Metro to demote Leinster to ninth place in the race for qualification at Thomond Park yesterday, adding salt to the open wound.
You could imagine Leinster players all over Dublin sitting at home, heads-in-hands, as they watched Munster being given the gift of the fifth-minute sending off of flanker Antoine Batut for making contact with the head of Keith Earls at a ruck.
From there, Munster flooded Racing with three tries in the second quarter, Ireland international Simon Zebo nailing the fourth and most meaningful nail into Leinster's coffin in the 48th minute.
Regrets? Leinster will have more than a few - none more so than their coach Joe Schmidt. The sheer quality of Pool Five meant it was highly unlikely that two clubs would emerge from it.
The spending power and unfathomable depth of Clermont's squad was bound to tell at some stage of their titanic struggles with Leinster. This is their time.
The choice of Romain Poite to handle the match at Sandy Park was always likely to elicit an eyes-to-the-sky response from Schmidt.
The Frenchman was a thorn lodged in Leinster's side in the 2012 PRO12 League final against the Ospreys, where his handling of the scrum and other facets were a source of frustration.
Schmidt had a question or 10 for Poite as both men made their way to the sanctuary of their dressing-rooms at half-time in Exeter on Saturday.
The source of this discussion or debate must have been the ruck resourcing of Leinster and what exactly Exeter did to disrupt them, players flying in from the side and off their feet at will.
That aside, Leinster will look back on the last quarter of their last two games and know that they did not do enough, convert enough possession into fives and sevens at home to The Scarlets and away to Exeter.
They had the bonus point secured by the 44th minute against the Welsh club; by the 53rd minute against the English.
For all the pressure they applied from those two points to the end, there was only one try, a late one from Ian Madigan against Scarlets, to show for the trouble they had gone to. They could not quite finish how they started both matches.
However, Schmidt was right to point at the competitive nature of the Chiefs as a significant hindrance to Leinster running up more than the four tries in a 29-20 win over the Premiership club.
"We knew how tough it was going to be to come here and get the five points, which was the minimum we required," he said.
"I thought we were really good for it, and the quality of our tries was first rate, but I have a lot of respect for Exeter as well.
"We are where we are. We can't control anything else that happens," Schmidt said on Saturday evening, adding that "Munster have a real target" because of the advantage of playing one day later than their provincial rivals.
Munster with a target was always likely to be akin to a dog with a bone. They just kept snarling, biting, gnawing away until they got what they wanted at home to a depleted Racing in Thomond Park yesterday afternoon.
Leinster were left to rue what might have been. Their carrot in Europe now is the Amlin Challenge Cup final at the RDS rather than the Heineken final at the Aviva Stadium. The test will be to muster the motivation necessary to travel to London Wasps for the quarter-final on the first weekend in April with the right attitude.