We knew it would come down to this. When the draw was made, Munster and Leinster were aware that the December double-headers would decide the pool. Now everything could be decided even before the second legs are played.
Leinster have easily the most difficult task, which has been compounded by the failure to get a bonus point at home to Exeter. In contrast, the French demolished the English team on their own turf.
Clermont are unbeaten in 50 games at the Stade Marcel Michelin. That's the equivalent of winning every single home game in the Top 14 for three seasons.
Joe Schmidt, as a former Clermont backs coach, had a considerable advantage facing his old side last season. He was able to highlight their weaknesses and tactics, and plan accordingly.
He has lost the element of surprise this time out, though, and Clermont coach Vern Cotter knows what to expect from Leinster now. Cotter has also developed and strengthened his squad, while Leinster if anything, have been weakened.
The Heineken Cup champions are still very weak in the second-row. Leo Cullen, although honest and hard-working, will have to cope alone with Clermont. Leinster have lost Brad Thorn from last season and have made poor signings in Tom Denton, who is out of his depth, and Quinn Roux, injured yet again, to replace him.
Devin Toner, despite countless opportunities, has never looked likely to step up to the level required.
Yet Leinster are unbeaten in 17 Heineken Cup games. The last time they lost in Europe was against Clermont in Stade Marcel Michelin two seasons ago. It is a winning habit that they will draw on in large measure
Clermont have two proven goal-kickers in their ranks, France scrum half Morgan Parra and Australian out-half Brock James. They back up an incredible squad. Nathan Hines, Julien Pierre, Julien Bonnaire, Jamie Cudmore, Vincent Debaty, Alexandre Lapandry and Elvis Vermeulen are all seasoned internationals.
The French outfit have never won the Heineken Cup. They were angry at last season's defeat in the semi-finals, when they seemed to have won it at the death. They have the personnel and management to humiliate a Leinster team who are weak and tired after five long seasons of success.
There is no logical basis other than home advantage for the bookmakers to make Munster favourites to win at Thomond Park. Saracens are not the most popular club in England because they play boring, one- dimensional rugby based on a rock-solid defence, but they do it better than any other side in Europe.
Incredibly, Saracens lie second in the Aviva Premiership with the worst try-scoring record in the league after 10 rounds. They have scored only nine tries in 10 games, compared to league leaders Harlequins who have managed 27.
However, Sarries have also conceded just nine tries and have the best defensive record in the league. Obviously, converting penalty chances is very much part of the game plan, predicated by a big, brutal and dangerous pack. Steve Borthwick, Mouritz Botha, Schalk Brits, Kelly Brown and John Smit have buckets of international experience. None of them will fear travelling to Thomond Park.
Despite their low try-scoring tally, Saracens have enough pace and power out wide to cause Munster some serious problems, with England internationals Owen Farrell, Brad Barritt, Alex Goode and Chris Ashton all capable of breaching the home defence.
Meanwhile, Munster coach Rob Penney does not appear to know his best starting XV. He began the season without his international players and he has been plagued by injury and withdrawals since then. The squad that began the Pro12 campaign played some exciting rugby, as epitomised by an opening win over Edinburgh in Murrayfield. But since then, it's been a mixed bag. Ronan O'Gara remains the first choice fly-half, despite not seeming to fit into Penney's game-plan.
The loss of Paul O'Connell is immense and the news of his return is as sketchy as ever. The line-out return has been poor in his absence and Munster could be exposed this weekend by a formidable Saracens pack.
Many people now fear that O'Connell may not be seen in action again – this would be a catastrophic loss to the province.
In his absence, CJ Stander could eventually prove to be a vital replacement in the pack. On his first start last week in the win over Glasgow, he showed he had incredible power and pace for a back-row forward, so it was a pity he picked up an injury.
Munster need a physical leader up front and their injury problems leave them lacking in physical presence, but they can win if they keep their discipline and not concede penalties.
However, one suspects the forwards will be 'under the cosh' and penalties will be given away as Saracens inflict their proven method of breaking down teams and grinding out wins.
Munster and Leinster will be digging deep into the memory bank of tradition and history this weekend. It may not be enough.