Cardiff Blues kept their Magners League title hopes alive by coming from behind to beat local rivals the Dragons 20-14 at Rodney Parade.
The Blues are just outside the top four play-off places. They could get through if the Ospreys beat Munster on Saturday and then they beat the Irishmen at Cardiff City Stadium in a fortnight.
The result almost certainly ends the Dragons' chances of reaching those play-offs unless they benefit from a mathematical miracle.
Both sides were hit by injuries and unavailability ahead of the match. Significantly, the Blues lost Wales international loose-head prop Gethin Jenkins with a foot injury plus flanker Martyn Williams and All Blacks centre Casey Laulala.
The Dragons lost five players from the squad that beat Edinburgh on Sunday, including talismanic outside-half Jason Tovey, who has concussion, and Wales international lock Luke Charteris.
And with a lot on the line for both teams including a play-off place and, most importantly, local bragging rights, neither side wanted to give an inch in the opening moments.
But, after Wales wing Leigh Halfpenny missed a long-range penalty in the opening minute, the Dragons went ahead when outside-half James Arlidge booted a penalty.
They then went 8-0 up when a move begun by skipper Tom Willis' drive ended with flanker Gavin Thomas feeding prop Ben Castle for an unconverted corner touchdown.
The match reached the interval as an average if intensely-fought affair.
Blues centre Jamie Roberts helped with the move that gave his side their first points when the Dragons infringed on their 22 for full-back Ben Blair to easily boot a penalty.
However, the Cardiff team lost an important component of their side when big number eight Andy Powell was led off the pitch with a calf injury, and that could be a worry for the Blues' Amlin Challenge Cup semi-final against London Wasps next Saturday.
The Dragons nearly got a second try when a surge into the Blues' 22 saw number eight Toby Faletau pick-up from a ruck and feed wing Will Harries for a corner touchdown but referee Alain Rolland ruled it out for a forward pass.
Head coach Dai Young must have given the Blues a stern word at half-time because they came out with more purpose after the break and forced the home region into mistakes.
From these, Blair had two kickable penalties but pushed both wide of the posts before taking his third opportunity from 20 metres when the Dragons strayed offside.
And finally the Blues had their say with two tries in the space of a few minutes on the hour mark that put distance between them and the Dragons.
It was former Dragons outside-half Ceri Sweeney who bagged the first of those two when he booted a high kick into the home 22 only for full-back Martyn Thomas to slip and allow Sweeney to re-capture the ball and score.
Then an excellent move down the right saw Halfpenny set up replacement Gavin Evans for a run-in.
Blair converted both to give his side a 20-8 lead going into the final quarter.
The Dragons suffered another big blow, with a clash against the Ospreys looming next week, when Thomas was stretchered off with a badly damaged ankle that saw him taken straight to hospital.
Another Arlidge penalty got the Dragons within sight of a losing bonus point and, deep into injury time, they achieved it with another penalty by the Kiwi.
For the Dragons:
Pens: Arlidge 3
For the Blues:
Tries: Sweeney, Evans
Cons: Blair 2
Dragons: 15 Martyn Thomas, 14 Will Harries, 13 Tom Riley, 12 Ashley Smith, 11 Richard Fussell, 10 James Arlidge, 9 Wayne Evans, 8 Toby Faletau, 7 Gavin Thomas, 6 Andrew Coombs, 5 Hoani MacDonald, 4 Rob Sidoli, 3 Ben Castle, 2 Tom Willis (c), 1 Hugh Gustafson.
Replacements: 16 Lloyd Burns, 17 Nigel Hall, 18 Lewis Evans, 19 James Harris, 20 Rhodri Gomer Davies, 21 Adam Hughes, 22 Alex Walker.
Cardiff Blues: 15 Ben Blair, 14 Leigh Halfpenny, 13 Jamie Roberts, 12 Dafydd Hewitt, 11 Chris Czekaj, 10 Ceri Sweeney, 9 Richie Rees, 8 Andy Powell, 7 Sam Warburton, 6 Maama Molitika, 5 Paul Tito, 4 Bradley Davies, 3 Scott Andrews, 2 T Rhys Thomas, 1 John Yapp.
Replacements: 16 Gareth Williams, 17 Taufa'au Filise, 18 Deiniol Jones, 19 Andries Pretorius, 20 Lloyd Williams, 21 Dai Flanagan, 22 Gavin Evans.
Referee: Alain Rolland