Montpellier ended a run of play-off defeats against Castres to book a place in the Top 14 semi-finals with a 28-9 triumph at Altrad Stadium.
Sunday's contest brought together two teams who had faced off in domestic knockout matches in four successive seasons from 2011, Castres winning the three most recent meetings.
However, European Challenge Cup winners Montpellier were not to be denied on this occasion as tries from Timoci Nagusa, Paul Willemse and Pierre Spies secured an ulttimately comfortable victory and a semi-final tie against Toulon.
Montpellier, who only dropped out of the top two in the final week of the regular season, opened up an 8-0 lead inside the first quarter, Nagusa barging over in the left corner following an early penalty from Demetri Catrakilis.
After Benjamin Urdapilleta had spurned a chance to reduce Castres' deficit from the tee, a sickening clash of heads between Anthony Tuitavake and Rodrigo Capo Ortega forced a lengthy delay. Ortega came off worse and was taken off on a stretcher, but the Castres lock was thankfully able to acknowledge the applause from the crowd as he left the field.
Catrakilis and Urdapilleta exchanged penalties prior to the interval, but a second Castres three-pointer early in the second half, from Rory Kockott, got the visitors back within five points.
Montpellier responded with a crucial score, Benoit Paillaugue's initial break followed by several effective carries that culminated in Willemse crossing from close range.
Although Kockott kicked his second penalty, Montpellier were able to pull further clear in the closing stages despite being reduced to 14 men when Jannie du Plessis was yellow-carded.
Catrakilis took his personal tally to 11 points with a penalty and then added two more after a break from Tuitavake enabled Spies to touch down and end the match as a contest.
The game ended on an unsavoury note, with players from both sides involved in a brief brawl.