Connacht will finish bottom of the Magners League after falling 27-14 to the Dragons in Newport on Sunday.
The Welsh side were deserved winners but should have collected a bonus point win against a very limited Connacht side.
It was a vital game for the Dragons as a loss would almost certainly have ended any hopes they had of securing automatic qualification for next season's Heineken Cup.
They were desperate to avenge their worst performance of the season, a 39-17 defeat at the hands of Connacht in Galway earlier this month.
The first 10 minutes were frenetic with regular turnovers and no pattern to the play.
Keith Matthews made a fine break for the visitors, slashing through a huge hole in the Dragons defence.
Richard Fussell, the Dragons wing, picked up a stray pass to cause problems to the Irish side but both movements fizzled out.
The home side had the first real opportunity for points but James Arlidge missed with a wide-angled penalty from 25 metres out.
The opening quarter was scoreless and featureless and it was easy to see why the teams are the bottom two in the Magners League.
It was yet another error which allowed the Dragons to build up some momentum.
Arlidge charged down Ian Keatley's kick to give the home side a line-out five metres from the line but in the process of scoring the Dragons pack knocked on under the Connacht posts and the visitors were able to relieve the pressure.
The Dragons continued to have the majority of possession and eventually took the lead after 35 minutes when Arlidge kicked a simple 30 metre penalty after Connacht were offside in midfield.
From the restart Connacht again offended, allowing Arlidge to place his penalty kick within five metres of the visitors' line.
From the line-out the Dragons produced a pre-planned move which allowed Joe Bearman to score. Arlidge converted to make it 10-0 at the interval.
Within a minute of the restart Connacht were dealt a further blow when their captain, Gavin Duffy, was sin-binned.
Referee Graham Knox evened things up moments later by yellow carding Rhodri Gomer-Davies for holding onto the ball after a tackle.
Connacht got their first real chance of points after 47 minutes but Keatley missed with a 40 metre penalty.
The outside half did make amends minutes later by running creatively to set up a try for Fionn Carr which Keatley converted.
Gomer-Davies returned from the sin-bin and within minutes he drove over from close range, which Arlidge converted to extend the Dragons' lead to 17-7 with a quarter of the match to go.
After 65 minutes the game was effectively over when Rhys Thomas scored near the posts. Arlidge again converted before adding another penalty with a well struck kick from near halfway.
Connacht showed they still had some life by producing a fine move for Keith Matthews to score which Keatley converted but any hopes of a comeback ended when Carr was sin-binned for holding back a Dragons player without the ball.
This enabled the Dragons to dominate the remainder of play as they went in search of their fourth try to secure a valuable bonus point but somehow the visitors' defence held out.
For the Dragons:
Tries: Bearman, Gomer Davies, Thomas
Cons: Arlidge 3
Pens: Arlidge 2
Tries: Carr, Matthews
Cons: Keatley 2
Dragons: 15 Jason Tovey, 14 Gareth Wyatt, 13 Rhodri Gomer Davies, 12 Ashley Smith, 11 Richard Fussell, 10 James Arlidge, 9 Wayne Evans, 8 Joe Bearman, 7 Richard Parks, 6 Danny Lydiate, 5 Luke Charteris, 4 Hoani Macdonald, 3 Rhys Thomas, 2 Tom Willis (c), 1 Adam Black.
Replacements: 16 Steve Jones, 17 Nigel Hall, 18 Andrew Hall, 19 Lewis Evans, 20 Martyn Thomas, 21 Rory Sidey, 22 Alex Walker.
Connacht: 15 Gavin Duffy (c), 14 Fionn Carr, 13 Niva Ta'auso, 12 Keith Matthews, 11 Liam Bibo, 10 Ian Keatley, 9 Frank Murphy, 8 Ray Ofisa, 7 Johnny O'Connor, 6 Andrew Browne, 5 Andrew Farley, 4 Michael Swift, 3 Brian McGovern, 2 Sean Cronin, 1 Brett Wilkinson.
Replacements: 16 Adrian Flavin, 17 Ray Loughney, 18 David Gannon, 19 Colm Rigney, 20 Conor O'Loughlin, 21 Andy Dunne, 22 Troy Nathan.
Referee: Graham Knox (Scotland)
Touch judges: Phil Fear (Wales), David Jones (Wales)
Television match official: Hugh Watkins (Wales)