Munster became the first team to book a place in the 2012 Heineken Cup quarter-finals on Saturday with a 26-10 win over Castres at Thomond Park.
Johne Murphy's converted try and four penalties from inspirational Ireland international Ronan O'Gara saw the hosts open up a 16-7 half-time lead, with Yannick Caballero responding for the visitors.
A tighter second-half followed with fly-halves O'Gara and Pierre Barnard trading three-pointers before Wian Du Preez secured their passage through to the next round.
Despite enduring a blip in last season's competition, failing to reach the quarter-finals for the first time in their history, the Limerick-based outfit have re-found their European form. The hosts only needed two points to guarantee their progression and they set their stall out early on with a Murphy touchdown.
O'Gara converted and then scored a penalty as the visitors struggled to cope with Munster's pace and power.
But a Castres side who sit bottom of Pool One hit back immediately through a Caballero try, Barnard adding the extras.
Two penalties from the home side's fly-half extended their lead to 16-7 at the break, but his opposite number reduced the gap to six points.
However, O'Gara added his fourth three-pointer as Munster reasserted their authority, and things got worse for the visitors when Thierry Lacrampe was sin-binned.
The hosts continued to press but made too many mistakes and struggled to break through some stubborn French defence.
But after they had finally put together a number of phases within the Castres 22, the unlikely figure of loosehead prop Du Preez powered over to confirm the win.
Tries: Murphy, du Preez
Cons: O'Gara 2
Pens: O'Gara 4
Yellow card: Lacrampe (Castres - 54th min)
Munster:15 Denis Hurley, 14 Johne Murphy, 13 Keith Earls, 12 Lifeimi Mafi, 11 Simon Zebo, 10 Ronan O'Gara, 9 Conor Murray, 8 James Coughlan, 7 Niall Ronan, 6 Peter O'Mahony, 5 Paul O'Connell (c), 4 Donnacha Ryan, 3 BJ Botha, 2 Damien Varley, 1 Wian du Preez.
Replacements: 16 Denis Fogarty, 17 Marcus Horan, 18 Stephen Archer, 19 Donncha O'Callaghan, 20 Billy Holland, 21 Tomas O'Leary, 22 Ian Keatley, 23 Danny Barnes.
Castres Olympique: 15 Romain Martial, 14 Vincent Inigo, 13 Paul Bonnefond, 12 Pierre-Manuel Garcia, 11 Pierre-Gilles Lakafia, 10 Pierre Bernard, 9 Thierry Lacrampe, 8 Jannie Bornman, 7 Steve Malonga, 6 Yannick Caballero, 5 Rodrigo Capo Ortega, 4 Matthias Rolland, 3 Anton Peikrishvili, 2 Marc-Antoine Rallier, 1 Saimone Taumoepeau.
Replacements: 16 Mathieu Bonello, 17 MichaÃ«l Coetzee, 18 Karena Wihongi, 19 Scott Murray, 20 Ibrahim Diarra, 21 Rory Kockott, 22 Seremaia Bai, 23 Matthieu Nicolas.
Venue:Thomond Park, Limerick
Referee: Andrew Small