Dragons earned a quarter-final spot in the European Challenge Cup as they secured a home bonus-point victory over Enisei-STM.
Scores from Ross Moriarty and Jared Rosser put the Dragons 14-5 up at half-time.
Harrison Keddie, Tyler Morgan, Aaron Wainwright and Adam Warren, with two, added second-half tries.
Castres' comeback in Worcester saw them win Pool One with Dragons finishing second.
The result from Sixways was of more concern than events at Rodney Parade once they had sealed the bonus point after 56 minutes.
Morgan dived over triumphantly for the fourth try, only to become one of three injury victims in the process with wings Jared Rosser and Rio Dyer also forced off.
The disjointed nature of the closing stages did not matter, but a high-scoring home win for Worcester could have knocked Dragons out.
A hat-trick of tries from Castres scrum-half Rory Kockott caused French and Welsh celebrations with the Dragons assured of being one of the best three second-placed sides.
Dragons flanker Keddie, a late call-up to the side, was man of the match as Dragons reached the knock-out stages for the first time since 2016.
More to follow.
Dragons: Carwyn Penny; Jared Rosser, Adam Warren, Tom Griffiths, Rio Dyer; Sam Davies, Tavis Knoyle; Lloyd Fairbrother, Elliot Dee, Leon Brown, Matthew Screech, Cory Hill (capt), Aaron Wainwright, Huw Taylor , Ross Moriarty.
Replacements: Ellis Shipp, Josh Reynolds, Chris Coleman, Joe Davies, Harrison Keddie, Luke Baldwin, Jacob Botica, Tyler Morgan.
Enisei-STM: Earll Douwrie; Davit Meskhi, David Kacharava, Dmitrii Gerasimov, Bjorn Basson; Ramil Gaisin, Alexey Shcherban; Nika Khatiashvili, Shamil Magomedov, Innokentiy Zykov, Uldis Saulite (capt), Evgeny Elgin, Mikheil Gachechiladze, Andrey Temnov Dmitrii Krotov.
Replacements: Stanislav Selskii, Ewald Westhuizen, Azat Musin, Jeremy Jordaan, Nikita Churashov, Konstantin Uzunov, Jurijs Baranovs, Vitaly Nemtsev.
Referee: Joy Neville (Ireland)
Assistants: Nigel Correll (Ireland) & Richard Kerr (Ireland)
TMO: Colin Stanley (Ireland)
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