Worcester Warriors conceded two tries as they lost to Castres in France in their second European Challenge Cup Pool One game.
Duncan Weir opened the scoring early on with the first of his three penalties.
But winger Filipo Nakosi and flanker Baptiste Delaporte both crossed before the break, prior to Weir's second kick.
Weir's third penalty pulled it back to 14-9 but a penalty for Benjamin Urdapilleta sealed Worcester's fate, denying them a losing bonus point.
Added to his earlier two successful conversions, the stand-off's individual seven-point haul proved the difference between the two teams to cost Worcester a potentially key extra point.
Worcester had five of their key injured players back, stand-off Weir, centre Ryan Mills and full-back Chris Pennell, who all started, while scrum-half Francois Hougaard and prop Nick Schonert came off the bench.
But their much-changed side could not build on the pool-opening 57-14 win over Enisei-STM in Russia, finishing with 14 men after club captain GJ van Velze was sinbinned.
Worcester now sit second in Pool One behind Dragons, who followed their opening 31-17 win over Castres by beating Enisei 49-22 in Krsasnodar on Friday night.
Mills skippered Worcester as he became only the 23rd Warriors player to reach 100 appearances for the club.
Castres: Palis; Nakosi, Combezou, Ebersohn, Paris; Urdapilleta, Kockott; Tichit, Rallier, Wihongi, Samson, Capo Ortega, Delaporte, Gerondeau, Tulou.
Replacements: Dumora for Palis (41), Jenneker for Rallier (47), Gimeno for Capo Ortega (48), Vaipulu for Gerondeau (58), Batlle for Nakosi (70), Fernandez for Kockott (77).
Not used: Fa'anunu, Hounkpatin.
Worcester Warriors: Pennell; Humphreys, Venter, Mills (capt), Fidow; Weir, Heaney; Waller, Annett, Carey, Bresler, Kitchener, Hill, Lewis, du Preez.
Replacements: Black for Waller (47), Moulds for Annett (53), van Velze for du Preez (53), Schonert for Carey (53), Shillcock for Pennell (58), Hougaard for Heaney (58), Lawrence for Venter (63), Clegg for Bresler (64).
Sin Bin: van Velze (70).
Referee: Sean Gallagher (Ireland).
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