Munster out-half JJ Hanrahan said he had anticipated an arm wrestle ahead of Munster's 25-point win over Castres in the Champions Cup meeting in Thomond Park.

Hanrahan was promoted to the starting XV shortly before kick off after Joey Carbery injured his hamstring in the lead-up to the game.

The Currow fly-half scored 20 points slipped over three penalties, three conversions and also ran in Munster's third try in the closing minutes. 

This teed up a frantic late drive for a bonus point but Munster ended the game on the defensive with replacement flanker Martin Laveau diving over for the visitors' only points in the dying seconds. 

Hanrahan told RTÉ Sport afterwards that stepping up at short notice was no major imposition as he knew he'd be involved at some stage. 

"I was named on the bench anyway so I knew I was going to be involved at some stage," he said. 

"It was unfortunate for Joey but between myself, Tyler (Bleyendaal), Bill (Johnston) and Keats (Ian Keatley), we're all ready to go and take our opportunities when they come. Sam Arnold had the same situation. The squad preps well and we're all over our details. 

"We knew it was going to be an arm wrestle. It was the exact same here last year when we played them at home. We were trying to back our tempo and fitness to take them later in the game. We said we could win it later in the game as opposed to the first 30. 

Hanrahan enjoyed a flawless afternoon off the kicking tee in awkward conditions

"I thought the front row were excellent today. The way they dominated at the scrum just makes our exit so much easier. We get a penalty at scrum and we can just bang it 30 yards down the field."

The swirling wind around Thomond didn't help the spectacle but Hanrahan was flawless from the kicking tee and he argues Munster's mastery of the basics saw them over the line. 

"It's a tricky one. Everyone knows in Thomond Park that it's a swirling wind. If you look at the flags on the pitch at one stage and they're flat and then the ones on the Stand are blowing. It was kind of blowing across the field. Hopefully, we might get better conditions next week. 

"Today was a day for the basics. It's an age old thing. Today was whoever did the basics well and I thought Murray kicked well off the base and relieved a bit of pressure. The boys were pretty good in the air and then we when we got a chance we put a bit of snap and tempo into the play, we did that as well." 

While Munster shipped come criticism for failing to convert chances, Hanrahan stresses Castres's pedigree and defensive solidity. 

"Their 13 was particularly good today. He was shooting up and cutting down a lot of options in fairness to him. We probably could have been a bit smarter there in the backline. We'll definitely study that and go again next week. Overall, we were happy to get them three tries in the second half. 

"We're going to their back garden now. It's a French side, full of passion, full of emotion. They're Top 14 champions. It's a hard place to go. We went there last year and got a draw. It was a very hard game for us. It's going to be the same this time."