Munster ran in five tries as they got their first Pool One points with a convincing win over French side Castres in Limerick.
HEINEKEN CUP, Pool 1
Munster (19) 42
Tries: O'Callaghan, Flannery, Horgan, Kelly, Halstead
Cons: O'Gara 4
Pens: O'Gara , Manning
Castres (13) 16
Pens: Marticorena 3
Victory was a must for Declan Kidney's side after losing to Sale on the opening weekend of the tournament.
Munster, quarter-finalists for the past seven seasons, got tries from Donncha O'Callaghan, Jerry Flannery, Anthony Horgan, John Kelly and Trevor Halstead.
Romain Teulet scored a try for Castres, who were just six behind at half-time.
The Irish province, quarter-finalists for the past seven seasons, scored their first try on six minutes as a traditional Munster maul up to the line saw lock O'Callaghan muscle over.
Another forward shunt on 18 minutes saw Flannery driven over for a second try.
Seven minutes later, winger Horgan was sent scurrying over in the left corner for his 14th Heineken Cup try and Munster seemed in dreamland at 19-6.
But a converted try for Teulet just before the break soon brought Declan Kidney's side back down to earth.
Their 19-13 half-time lead was cut 10 minutes into the second half as Laurent Marticorena made it a three-point game with his third penalty.
But Munster turned on the power to secure victory.
O'Gara landed two penalties fro more than 40 metres to give Kidney's men a degree of comfort at 25-16 before Kelly grabbed the bonus point score.
A delightful crossfield kick to the right wing from O'Gara's see winger Kelly storm up, collect it and dip under Marticorena's corner flag tackle to score.
On 72 minutes, South African centre Halstead stepped inside Phil Christophers, having been set up by former Great Britain rugby league star Gary Connolly, to grab Munster's fifth try.
Munster hooker Jerry Flannery:
"It was brilliant. There was a lot of talk in the newspapers about this being a do-or-die match for us. But with the crowd here behind us, we're always confident.
"We've played Castres often enough over the years to know what a quality side they are and they deserve credit for coming back to three points down.
"The five tries won us the game but I thought our defence was superb. Graham Steadman has put a lot of work in with us in defence and it paid off in the last 15 minutes."
Munster: Payne, Kelly, Connolly, Halstead, Horgan, O'Gara, Stringer, Horan, Flannery, Hayes, O'Callaghan, O'Driscoll, Leamy, Wallace, Foley.
Replacements: B. Murphy for Connolly (80), Manning for O'Gara (80), O'Leary for Stringer (80), Fogarty for Flannery (80), Hogan for O'Driscoll (80), S. Keogh for Foley (80).
Castres: Peyras-Loustalet, Milford, Marticorena, Tuilagi, Christophers, Teulet, Barrau, Hoeft, Vigneaux, Meeuws, Spanghero, Nallet, Puricelli, Volley, Faure.
Replacements: Forestier for Milford (69), Raffault for Tuilagi (32), Albouy for Barrau (62), Capo Ortega for Spanghero (55), Taussac for Faure (67).
Referee: Dave Pearson (RFU).