Leinster head coach Matt O'Connor felt his side "got out of jail" in denying Castres from picking up a bonus point at the RDS.
The Irish province made it two wins from two in Pool 1 of this season's Heineken Cup after they battled to a 19-7 triumph over their Top 14 opponents on Saturday.
Crucially they also denied the visitors picking up a losing bonus, albeit by the smallest possible margin after Pedrie Wannenburg had a try ruled out by the Television Match Official with two minutes remaining.
"I certainly think we got out of jail with regard to them getting nothing (no bonus point). I don't think we got out of jail with regards to the result," O'Connor said.
"In the first half we were, by far, the better side. They got a lucky score and we didn't capitalise on our opportunities. They came back hard in the second half but we'll take the four points.
"Castres are a quality side. They are physically massive as a group. You don't fluke it and win the Top 14 unless you've got a really good squad. We put a lot of holes in them but didn't capitalise.
"It is one of those things. You take the four points and make sure we are better next time."
Referring to Wannenburg's close call with three minutes left on the clock, O'Connor conceded: "It wasn't a great camera angle and you couldn't really tell as you couldn't see it being scored. You'd have to ask the guys out there but it wasn't obvious on camera."
A 62nd minute try from replacement prop Jack McGrath, after Castres lost centre Remi Lamerat to the sin-bin proved crucial, though visiting captain Remi Tales felt there were some positives to take out of the defeat.
"We held our own against a really good team," he said. "We must remember this game and how well we played, when we face them again at home in January."