After conquering the continent under Warren Gatland in 2004 when Rob Howley performed his last-minute grand larceny on Toulouse at the expense of Clement Poitrenaud, the champions slumped to third in their pool the following season.
They were at least in company, finishing behind Biarritz and Leicester.
The same fate befell Wasps three years later. After recapturing the Heineken Cup under Sir Ian McGeechan, they found themselves swimming in a pool the following season alongside two of the biggest fish, Munster and Clermont.
When the dust settled on the six-round pool stage, Wasps wound up in third place, one point behind their Irish and French rivals.
Should Leinster lose to the Scarlets at the RDS this Saturday or to Exeter in Devon the following week, they will be the first champions since Wasps to lose their title without getting as far as the quarter-finals.
The idea of the holders being counted out at such a premature stage would have been unthinkable going into December.
Those heavyweight skirmishes with Clermont on successive weekends may yet change the course of history. A losing bonus point in central France and another in Dublin have left the jewel in the RaboDirect PRO12 crown needing a maximum ten from their two remaining matches if they are to catch the last boat into the quarters as one of the two best runners-up.
The Scarlets are already out and licking their wounds from last week's exposure to Ulster at Ravenhill where they shipped 47 points on top of the 32 from their previous match, against the Ospreys in Swansea on Boxing Day.
Leinster, therefore, ought to ensure they are still in with a fighting chance when they go to Devon the following Saturday for their return against the West Country Chiefs.
Elsewhere other PRO12 clubs are involved in critical matches, starting on Friday night.
Ulster, shaken by Northampton's stunning win in Belfast before Christmas, will clinch their qualification provided they take all five points from Glasgow at Ravenhill and Northampton fall short of doing likewise against Castres at Franklin's Gardens on the same evening.
Clermont will be through on Saturday unless Exeter do what nobody has done for more than three years and win at the Stade Marcel Michelin.
After more than 50 straight home wins there for the best team not to have won the European Cup, an English victory would be the mother-and-father of all upsets, even allowing for Exeter's soaring rise under head coach Rob Baxter.
Sunday brings two matches of colossal significance with the fate of two PRO12 contenders on the line. Munster, down to third in Pool 1 after losing their away match to Saracens, go to Edinburgh where last year's semi-finalists have neither a point nor a try to show for four defeats.
If Sarries find Racing in Paris too hot to handle, Munster might yet find themselves back in charge of their own destiny with the final game at home - Racing at Thomond Park.
The Parisians made a mighty declaration of intent last weekend, going down to the Mediterranean and beating Toulon whose stellar cast had not lost at home all season.
Ospreys gave Pool 2 a mighty shake by beating Toulouse 17-6 before Christmas. Now they must rattle the Tigers' cage and ensure the five-time finalists take no liberties at the Liberty.
If the last eight is not to be a Welsh-free zone for the second time in three seasons, nothing less than a home win will be good enough.
This will be the eighth European tie between the best of Anglo-Welsh rivals in seven seasons. Their record includes an unforgettable draw (32-32) at Welford Road three years ago when Leicester came from a long way behind. More significantly, their last three duels in Swansea have been in the balance until the last second.
Leicester won there 17-15 in 2005 but have lost on both subsequent visits - 15-9 in 2009 and 17-12 the following year.
With no margin for error, the only Welsh region to win in the competition this season must make it three-in-a-row or join the Blues and Scarlets among the also-rans.
Toulouse, one point behind Leicester in second place and home to Treviso, have only one try to show for their last four matches, all away, and that from 34-year-old player-coach, William Servat.
While their rivals are otherwise engaged knocking seven bells out of each other in Swansea, the French champions need a decisive win with the prospect of a winner-take-all decider looming at Welford Road next weekend.
In the frantic rush to reach the knock-out stage as the two best runners-up, 20 points may not necessarily be enough. Since the introduction of the current points system in 2003, only two teams have qualified with 19 points.
The full list of best runners-up:
Last season: Cardiff Blues 21 pts, Ulster 20.
2010-11: Ulster 22, Leicester Tigers 22.
2009-10: Ospreys 20, Northampton Saints 19.
2008-09: Toulouse 20, Ospreys 20.
2007-08: Perpignan 22, Ospreys 21.
2006-07: Munster 23, Northampton Saints 20.
2005-06: Sale Sharks 23, Leinster 22.
2004-05: Northampton Saints 21, Leicester Tigers 19.
2003-04: Gloucester 24, Edinburgh 22.
Top six seeds as they stand:
1 Harlequins 19 pts (21 tries)
2 Toulon 18 pts (16 tries)
3 Clermont Auvergne 18 pts (13 tries)
4 Ulster 15 pts (9 tries)
5 Leicester Tigers 14 pts (11 tries)
6 Saracens 14 pts (9 tries)
Best runners-up as they stand:
Montpellier 13 pts (11 tries)
Toulouse 13 pts (9 tries)
Castres Olympique 12 pts (5 tries)
Racing Metro 12 pts (4 tries)
Leinster 10 pts (3 tries)
Biarritz Olympique 9 pts (10 tries)
Currently third but still alive:
Munster 11 pts (7 tries)
Northampton Saints 10 pts (6 tries)
Ospreys 9 pts (8 tries)
Exeter Chiefs 9 pts (4 tries)
Already out:
Edinburgh, Benetton Treviso, Zebre, Glasgow Warriors, Scarlets, Sale Sharks, Cardiff Blues.
Last chance saloon:
Racing Metro, Munster, Ospreys, Biarritz Olympique, Castres, Northampton Saints, Leinster, Exeter Chiefs.
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