text: Blues built a 14-3 lead with tries by Lloyd Williams and Gareth Anscombe.
  Hallam Amos hit back before the break, Nic Cudd followed up and they earned a penalty try.
  Josh Navidi went over as Blues staged a late challenge, but the hosts held on to earn a last-four clash with Edinburgh.
  The talking points began well before kick-off.
  Dragons boss Lyn Jones named Wales number eight Taulupe Faletau on the bench with Nick Crosswell preferred in their starting back-row.
  Blues picked former Wales and British and Irish Lions prop Adam Jones on the bench and they suffered a late blow when Argentine Joaquin Tuculet failed a fitness test.
  Scrum-half Tavis Knoyle took over at centre with Lewis Jones coming on to the bench while Scott Andrews was picked at tight-head ahead of Jones.
  That meant four of the Blues' changes were enforced, with fly-half Rhys Patchell, centre Cory Allen and makeshift midfielder Tuculet injured and Lucas Amorosino ineligible.
  The opening period belonged to the visitors as they built a 14-3 lead by exploiting Dragons' defensive frailties.
  Jones' side were exposed time and again through fly-half Anscombe, wing Alex Cuthbert and scrum-half Williams.
  When centre Jack Dixon allowed Cuthbert a gap, the wing set up the ruck from which Williams squeezed over and Anscombe added the extras.
  Wing Tom Prydie kicked Dragons' first points, a penalty before Anscombe's try extended the Blues' lead.
  This time the New Zealand-born Wales hopeful made the most of a hesitant home defence to dart over, again converting.
  Dragons' fightback began when Anscombe returned the favour to the hosts by picking the wrong defensive line.
  Anscombe was attracted by Jack Dixon's presence to allow wing Amos the time and space to burst clear.
  Prydie's conversion made it 14-10 to the Blues at the break.
  Poor line-out defence allowed Dragons to seize the initiative and after Faletau led the phase-play charge, replacement flanker Cudd reached the line.
  Blues' implosion continued as Jonathan Evans charged down Williams' clearance.
  The visiting scrum-half then tried to drag his opposite number back and referee JP Doyle awarded the penalty try, converted by Prydie
  Williams was also sin-binned, but was back as Blues launched their late effort to regain the lead after home fly-half Dorian Jones' penalty.
  A dominant scrum allowed Navidi to touch down and Anscombe to convert, but Dragons thwarted Blues' final assault to seal victory.
  NG Dragons: Jason Tovey; Tom Prydie, Pat Leach, Jack Dixon, Hallam Amos; Dorian Jones, Jonathan Evans; Phil Price, T Rhys Thomas (capt), Brok Harris, Andrew Coombs, Cory Hill, James Thomas, James Benjamin, Nick Crosswell.
  Replacements: Hugh Gustafson, Lloyd Fairbrother, Dan Way, Taulupe Faletau, Nic Cudd, Luc Jones, Tyler Morgan, Geraint Rhys Jones.
  Cardiff Blues: Dan Fish; Alex Cuthbert, Gavin Evans, Tavis Knoyle, Richard Smith; Gareth Anscombe, Lloyd Williams; Gethin Jenkins, Matthew Rees (capt), Scott Andrews, Jarrad Hoeata, Lou Reed, Josh Turnbull, Sam Warburton, Josh Navidi.
  Replacements: Kristian Dacey, Sam Hobbs, Adam Jones, Macauley Cook, Ellis Jenkins, Lewis Jones, Simon Humberstone, Gareth Davies.
  Referee: JP Doyle (England)
  Assistant referees:  Greg Garner (England), Matthew Carley (England).
  Fourth Official: Barrie Gregory (Wales)
  TMO: Graham Hughes (England)
  Citing Commissioner: Shaun Gallagher (England)
target: Newport Gwent Dragons staged a dramatic fightback before holding off Cardiff Blues to reach the European Challenge Cup semi-finals.