Clermont slumped to a 16-13 defeat at Castres on Friday as the French Top 14 leaders failed to end their 36-year wait for a win at their opponents' Stade Pierre Antoine fortress.
Clermont had looked on course to break that miserable record when they led 13-6 early in the second half, but Castres battled back and snatched victory with five minutes left with a penalty from replacement full-back Romain Tuelet.
The league leaders were 6-3 up at the interval thanks to a 40-metre penalty from Australian fly-half Brock James and another three-pointer from scrum-half Ludovic Radosavljevic.
The Clermont scrum-half had already missed an optimistic drop goal attempt before taking over the kicking duties from James who was sin-binned later in the first period for a dangerous tackle on Castres' Kiwi centre Daniel Kirkpatrick.
South African scrum-half Rory Kockott kicked Castres' only reply, a small consolation after the former Sharks star had missed four attempts at goal.
The 26-year-old Kockott was on target early in the second half to bring the scores level at 6-6 before Clermont grabbed the opening try of the game after 50 minutes.
But it came in controversial circumstances.
Castres, who were pushing for a score of their own, were furious that James wasn't punished for another high tackle, this time on winger Marc Andreu.
Clermont's fullback Jean-Marcelin Buttin (R) scores a try during the Top 14 rugby union match at the Pierre-Antoine stadium in Castres, southwestern France. Clermont slumped to a 16-13 defeat at Castres.
South African lock Jan Bornman then clumsily lost possession to Clermont full-back Jean Marcelin Buttin who sprinted 80 metres to score a fine breakaway try.
James added the extras for a 13-6 lead.
Kockott then missed his fifth penalty of the night before the South African made up for his misfiring boot by scoring the try which brought his team back into the match on 63 minutes.
Replacement flanker Antonie Claassen created the try by bursting through the line to set-up Kockott who burrowed over from close range.
Tuelet added the conversion to level the scores at 13-13.
With five minutes left, Castres nipped ahead for the first time with a Teulet penalty awarded after Clermont replacement centre Wesley Fofana was punished for a deliberate knock-on as the home side ratcheted up the pressure.
Teulet then missed a last-minute penalty, but it didn't matter as his team preserved their undefeated home record this season.