Leinster forwards coach Jono Gibbes hailed a gutsy recovery from the Irish side as they ended Castres' proud 18-match home record at Stade Pierre-Antoine with a 29-22 victory.
The Heineken Cup Pool One leaders were staring at their second successive European defeat after Richie Gray and Brice Dulin touched down for a 14-0 Castres lead after 20 minutes.
But 21-point fly-half Jimmy Gopperth inspired Leinster's comeback, scoring two first-half tries with man-of-the-match Rob Kearney chipping in with a drop goal and Jordi Murphy adding a clinching late try.
"Castres delivered everything we thought they would - they were massively combative, very physical at the breakdown and a good set-piece," said Gibbes.
"It took a massive effort from us to score three tries and we almost sniffed out an opportunity for a fourth at the end.
"To come to a place like this against a well-organised team that haven't given up a lot of tries at home, it's a satisfying result and puts a spring in our step for next week."
Commenting on his side's early lapses, the New Zealander admitted: "It wasn't an ideal start.
"The way they were able to gain access was more about our deficiencies rather than them creating a hell of a lot - but they're a good team, we gave them a little bit and they took those two tries early.
"We just felt if we were able to get a little bit of a foothold with possession, particularly at set-piece, that we may be able to put pressure on them later on... and it took quite a long time to do that.
"I thought the boys' resilience and energy and their commitment to keep getting up and running into these big fellas here was first class."
Leinster now need just one match point at home to the Ospreys next Friday to qualify for the last eight as pool winners.
They are four points ahead of second-placed Northampton Saints, who host Castres in round six and Gopperth is eyeing up another win to seal a home quarter-final.
"Of course you want a home quarter and to achieve that we've got to win the game next week," said the Kiwi number 10.
"We've just got to make sure we get the points on the board early, make sure we win first and let the game take care of itself after that.
"Hopefully we'll get a good outcome from it."
Castres fly-half Remi Tales, who had to go off in the first half with a bicep injury, said that Leinster's big-game experience counted for them at crucial stages.
"It's a shame. The smallest error was punished. We're disappointed because overall we played a good match," he said.
"They're a team with huge experience. In key moments, that makes the difference."
David Darricarrere, who coaches the Top 14 club along with Serge Milhas, pointed to the 'small inaccuracies' that Leinster seized upon to turn the game in their favour.
"We were in a good place in the first half, but Leinster capitalised on our mistakes and handling errors and the little details that matter at this level," he said.
"They don't make a lot of mistakes and their Heineken Cup experience stood to them. We still have a game to play against Northampton and there will be no let-up from us.
"We're learn from today and I believe matches like these - played at such a pace and intensity - will prepare us well for rest of the Top 14 Championship."