Ronan O’Gara, who became the most capped player in the Heineken Cup with his 102^nd appearance and scored in his 85^th consecutive game in the tournament, proved his side’s talisman once again.

The Ireland fly-half’s reliable boot proved the difference with his personal haul of 16 points against a Castres side which had nothing to play for but pride and refused to lie down.

Munster will travel to the MK Stadium to face a resurgent Northampton Saints in the final game of the Pool next weekend determined to keep their unbeaten record so far this season and to notch up a clean sweep of wins.

The home side couldn’t have asked for a better start when wing Johne Murphy crashed over after only eight minutes to calm the nerves of a sell-out and expectant home crowd in Limerick.

But they were soon stunned into silence when Castres, completely against the run of play, managed a try of their own from a quick tap penalty when blindside flanker Yannick Caballero slipped over from short-range.

O’Gara settled his side’s nerves with two quick penalties to make it 16-7 midway through the first half to give them the lead at half-time but the French side made them work hard for every point.

Outside half Pierre Bernard landed an outrageous penalty on the halfway line to claw Castres back to within six points just after the break before O’Gara replied with his fourth penalty to make it 19-10.

Castres then went down 14-men when they had scrum-half Thierry Lacrampe sin-binned for a professional foul but the home side failed to take advantage and didn’t manage a point during their spell with an extra-man.

But when Munster’s second try came, it was after a break by centre Lifemi Mafi which led to prop Wian Du Preez burrowing his way over the line to make it five wins out of five in this season’s tournament.