Cardiff Blues' play-off ambitions hang in the balance after the Dragons recorded a shock 28-15 victory at Rodney Parade on Friday.
With one round remaining Cardiff have to travel to fellow top-four contenders, the Scarlets, while the Ospreys are away to bottom-of-the-table dwellers Aironi.
Although the visitors came back from 12 points down to level at 15-15 thanks to scores from back-rowers Sam Warburton and Xavier Rush, Newport's Andrew Coombs came off the bench to touch down for the decisive try.
Unbeaten in their last eight encounters against the Dragons, the Blues set out to extend that run and duly took an early lead through fly-half Dan Parks.
But the Men from Gwent tend to lift their game for the Welsh local derbies and hit back with a debut try from full-back Stefan Jones. The youngster showed impressive pace and then threw an audacious dummy to eventually score, with stand-off Jason Tovey adding a superb conversion from out wide.
After 13 minutes, Tovey was in inspired form once more when his perfectly weighted cross-kick was collected by lock Luke
Charteris, who fed inside to winger Aled Brew. Tovey missed the conversion but kicked a penalty to take their lead to 15-3.
However, five minutes before half-time Cardiff pressed and Dragons' second-row Adam Jones was subsequently sin-binned for cynically slowing the ball down.
From the resultant scrum Warburton powered over and Parks added the extras to leave the match finely poised at the break. Cardiff went on the attack immediately into the second period and were rewarded when Rush touched down from a driving maul.
Parks, who was having a poor day with the boot, hit the post with a relatively simple conversion. With 15 minutes to go Coombs burrowed over for the Dragons' third try and Tovey converted.
And the hosts confirmed victory when full-back Jones kicked a long penalty before scrum-half Wayne Evans scored a last minute drop-goal to take the Blues out of losing bonus-point territory.
Tries: S. Jones, Brew, Coombs
Cons: Tovey 2
Pens: Tovey, S. Jones
Tries: Warburton, Rush
Yellow card: Adam Jones ( Dragons - 36th min)
Dragons: 15 Stefan Jones, 14 Adam Hughes, 13 Tom Riley, 12 Ashley Smith, 11 Aled Brew, 10 Jason Tovey, 9 Wayne Evans, 8 Toby Faletau, 7 Gavin Thomas, 6 Danny Lydiate, 5 Adam Jones, 4 Luke Charteris (capt), 3 Ben Castle, 2 Lloyd Burns, 1 Phil Price.
Replacements: 16 Tom Willis, 17 Hugh Gustafson, 18 Dan Way, 19 Andrew Coombs, 20 Lewis Evans, 21 Pat Leach, 22 Jonathan Evans, 23 Mathew Jones.
Cardiff Blues: 15 Dan Fish, 14 Chris Czekaj, 13 Casey Laulala, 12 Jamie Roberts, 11 Tom James, 10 Dan Parks, 9 Richie Rees, 8 Xavier Rush, 7 Sam Warburton/Ben White, 6 Michael Paterson, 5 Paul Tito (capt), 4 Bradley Davies, 3 Taufa'ao Filise, 2 Gareth Williams, 1 John Yapp.
Replacements: 16 Rhys Williams, 17 Sam Hobbs, 18 Scott Andrews, 19 Deiniol Jones, 20 Ma'ama Molitika, 21 Lloyd Williams, 22 Ceri Sweeney, 23 Dafydd Hewitt.
Venue: Rodney Parade
Referee: James Jones (Wales)
Assistant Referees: David Jones (Wales), Hugh Watkins (Wales)