Champions Toulouse were unconvincing as they stretched their unbeaten record in the pool stages yesterday.
Captain Thierry Dusautoir scored in each half, either side of Vincent Clerc's 32nd try of the competition, although the Frenchmen failed to collect a bonus against the pool's bottom side.
Jason Tovey scored the only points for the Dragons with a penalty just before half-time, but the Welsh club came away from Stade Ernest-Wallon having earned credit for their defensive display.
A frustrating afternoon for the cup holders was capped by the sight of Frederic Michalak shown a yellow card late on, just moments after returning from a long-term injury.
The Dragons had flanker Dan Lydiate back from injury and faced a Toulouse team missing former All Blacks scrum-half Byron Kelleher but still boasting 14 internationals in their starting line-up.
Toulouse heaped pressure on the Dragons from the opening exchanges but the Welsh visitors survived a series of scrums close to their own line and it was their outside-half Tovey who had the first attempt at goal, off-target after five minutes.
The power of the Toulouse pack was obvious from the start and it was through their forwards that the opening try came in the 12th minute. Prop Census Johnston followed David Skrela's burst before captain Dusautoir drove over.
However, that did not mark the opening of the floodgates and it was not for another 23 minutes that Toulouse found their way through for a second try.
Clerc, top try-scorer in the competition, finished Clement Poitrenaud's attack to grab the 32nd European score of his career.
However, Skrela was off-target again with the conversion, having missed the first, and when Jean-Baptiste Poux was caught offside, Tovey kicked his penalty to keep the Dragons in touch, the Welsh side trailing 10-3 at the interval.
The second half saw more of the same for Toulouse, who dominated possession and territory yet failed to turn either into points.
Cedric Heymans was beaten to his own kick by Tovey while Johnston was penalised after Toulouse had opted to go for a scrum five yards from the Dragons try-line.
Man of the match Poitrenaud looked to have opened the door for a third try only for Dusautoir and Florian Fritz to get in each other's way in trying to receive the scoring pass.
That score finally arrived 11 minutes from the end of the match when Dusautoir was at the tail of an impressive lineout drive that crossed from 10 metres out.
Skrela converted before being replaced by Michalak, only for the the replacement to see a yellow card for deliberately knocking down Wayne Evans' pass.
Scorers -- Toulouse: Dusautoir 2 tries; Clerc try, Skrela con. Dragons: Tovey pen.
Toulouse: M Medard (F Fritz 58); V Clerc; Y Jauzion, C Poitrenaud, C Heymans; D Skrela (F Michalak 70), N Vergallo (J Doussain 70); J Poux (D Human 50), V Lacombe (W Servat 50), C Johnston, G Lamboley (Y Maestri 58), P Albacete, J Bouilhou, T Dusautoir (capt), S Sowerby.
Dragons: W Harries; N Brew, A Hughes, A Smith (P Leach 74), A Brew; J Tovey, W Evans; P Price, T Willis (capt, S Jones 61), B Castle (P Palmer 76), L Charteris, S Morgan (R Sidoli 61), D Lydiate, G Thomas (A Coombs 72), T Faletau.
Referee: P Fitzgibbon (Ire).
Sunday Indo Sport