Leinster forwards coach Jono Gibbes hailed a massive effort from the three-time champions to come from behind away to Castres.
The Irish side found themselves 14-0 down after tries from Richie Gray and Brice Dulin put the Top 14 champions ahead.
But 21 points from Leinster fly-half Jimmy Gopperth, who scored two tries, swung the momentum back in the visitors' favour for a 29-22 win.
"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."
Gibbes highlighted Leinster's flaws as the reason for Castres scoring freely so early on, stating that once Leinster began to control the set-piece the result followed.
"It wasn't an ideal start," added Gibbes.
"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."
Gopperth, who joined Leinster from Newcastle Falcons this season, said that the immediate focus was on getting the win against the Ospreys this weekend, with the bonus point possibly needed for a home quarter-final following afterwards.
"Of course you want a home quarter-final and to achieve that we've got to win the game next week," said Gopperth.
"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.
"We were disappointed with missing a couple of first-up tackles that got us into that situation (of being 14-0 down).
"It's the belief in each other and wanting to work hard for each other.
"Leinster have always been a great scrambling team and I think we just worked hard for each other because we want to be in the top eight.
"Our set-piece took a bit of a hard knock and they got their act into gear and we really got some go-forward ball and looked after it in the second half. That's when we created opportunities and we finished well."