When you know how to win you don't know how to lose. Given a fearful buffeting early on at the Stade Pierre-Antoine on Saturday night, and grateful enough to be just 20-6 down at one point, Munster went and did it again. It is doubtful whether any Irish side could have conjured a result like this, the latest in Munster's list of famous wins. Maybe they just like a challenge.

The perceived strengths of English and French sides are overrated, and ultimately Castres flattered to deceive big time. Not for the first time French mental strength proved questionable under pressure, but what must have been equally alarming for them was their comparative lack of fitness and defensive organisation out wide. Munster utterly outlasted opponents who used 20 players, replenishing four of their tight five. Munster, on the other hand, used the same 15 who started the game - and were even reduced to 14 men for 10 minutes before the break.

Even so, it was the type of game Munster would have lost a couple of years back. In fact they did. For this was uncannily like their quarter-final exit two seasons ago in Colomiers. Then, as on Saturday night, they conceded a seven-pointer inside the second minute and the scoring pattern was exactly the same up to the point where they trailed 20-9.

Similarly too, the home side had targeted the Munster scrum with unnerving success, as the referee and his assistants again struggled to cope with the pace of the game and the off-the-ball incidents. There were even signs of Munster's discipline cracking under the strain.

Munster had themselves targeted the Castres scrum, but as a result were caught cold at the first put-in when Alexandre Albouy sniped up the blind side from inside his own 10-metre line, though the sweeping try was finished off in the far corner by Philippe Garrigues following a couple of undetected forward passes.

The undetected blind-side obstruction to clear a path for Albert Costes' untouched run to the line for Castres' second try was almost risible. Likewise, Castres' scrummaging technique of driving upwards was suspicious and they lived offside on the fringes and in midfield.

Munster conceded three untypical penalties, the third of which saw a penalty reversed and Alan Quinlan sin-binned for shifting a Castres body off the ball after the whistle. The typical sleeves-rolled-up response in the next seven-man scrum and a scoreless 10-minute spell was something of a turning point.

Crucially though, Guillaume Delmotte wasted a three-on-one on half-way at 20-6, while Ronan O'Gara kept Munster's scorecard ticking. As it transpired, Declan Kidney wasn't that concerned at the interval.

"I thought when we were on the ball we were very good. The trouble was, when we weren't on the ball I was disappointed with a few things, such as the obstruction for the second try. You just wondered would the thing snowball and everything go against you on the one day.

"The way we were playing was okay, it was a case of could we dig our way out of trouble, could we get the first score and have the patience then. Rugby is becoming more chess-like now. Give yourself 10 minutes to get a score, give yourself another 10 minutes to get a score, and then have the calmness to go for the tries." Such calmness in a crisis transmits itself throughout the Munster set-up, the Kidney rationale being: "Why panic? It doesn't exactly improve your situation in any part of your life, and sport mirrors life sometimes."

So whereas Colomiers rode out 23-9 winners two years ago in a fractious and scoreless second period, this time Munster kept their nerve, remained patient, and nibbled steadily into Castres' nerves and their lead. They also nibbled into the Castres lineout, where Quinlan redeemed himself by stealthily nicking a couple of balls. They ran back the restarts with gusto, locked the scrum, kept the ball in the hand and rucked Castres off the park, with Frankie Sheahan giving a fine performance.

After a typically dogged foot-rush try by Dominic Crotty, Munster manufactured two cracking tries to deservedly win the game. O'Gara's flat cut-out pass for Anthony Horgan's try after Quinlan had made the hard yards was a beauty, and superbly taken by the winger. Things improved further when the Munster pack recycled another safety-first long restart by Gregor Townsend. The ball was moved wide to David Wallace in an outside centre position, and his half-break was supported on the inside by Holland, who broke through from inside the 22 to almost halfway and offloaded off the deck. A finger tip, one-touch transfer by Crotty was taken on by O'Gara, who used the support runners to go all the way himself and then convert. Shades of his and Munster's game-breaking try against Toulouse in last season's semi-final.

"We should never have lost that game," lamented Castres' Jeremy Davidson. "But they play out of the tackle very well and that try was like the one they scored in Bordeaux. They've a real touch of class when they play like that and they deserved it completely just for that try."

Though the crowd had howled angrily at times, the cacophony of sound perhaps distracting O'Gara as he missed five of his 10 kicks, ultimately even they were reduced to first stunned silence and finally respectful applause and sporting acknowledgement. Just like Stade de France and Bordeaux last season. After the decades of hurt, these sorties to France are becoming fun.

Castres: F Plisson; U Mola, E Artiguste, G Delmotte, P Garrigues; G Townsend, A Albouy; M Reggiardo, R Vigneux, L Tsabadze, S Chinarro, J Davidson (capt), A Coste, I Lassissi, J Diaz. Replacements - C Batut for Vigneux (61 mins), D Dima for Reggiardo (61 mins), G Benazet for Tsabadze (52 mins), F Laluque for Chinarro (47 mins), G Taussec, A Larkin, F Seguier.

Munster: D Crotty; J Kelly, M Mullins, J Langford, A Horgan; R O'Gara, P Stringer; P Clohessy, F Sheahan, J Hayes, M Galwey (capt), J Langford, A Quinlan, A Foley, D Wallace. Replacements - M Horan, J Blaney, M O'Driscoll, C McMahon, T Tierney, J Staunton, J O'Neill. Referee: G Simmonds (Wales).

Sin binned: A Quinlan (Munster) 30-40 mins.