The Ospreys came from behind after a scoreless first half to defeat the Dragons 20-10 at the Millennium Stadium in Cardiff.
Steve Tandy's men dominated the opening period but failed to find a way through some stout Dragons' defence as the half ended scoreless.
The second period proved to be a livelier affair, even if it didn't quite match the 30,411 crowd which had turned out for 'Judgement Day.'
It was the Dragons that took the lead through Richie Rees before a Dan Biggar penalty and a converted Tom Habberfield try took the Ospreys ahead.
Tom Prydie levelled matters from the tee, but another Biggar three-pointer and a penalty try snatched the victory.
With the Glasgow Warriors showing an upturn in fortunes over recent weeks, the Ospreys ideally wanted a bonus-point win to put pressure on the Scottish team. However, they were wasteful in the opening period.
Hanno Dirksen went close in the early exchanges before Richard Fussell appeared to have touched down, but play was called back for a knock-on from Habberfield.
It summed up a disappointing first half from the Swansea-based outfit. A combination of an excellent Newport rearguard and poor basic skills contributed to an error-strewn game.
The top-four contenders certainly had their opportunities and Dan Baker was next to try his luck, but the number eight lost possession of the ball with the line at his mercy.
Lyn Jones' side very rarely tested their opponents but, when they did, lock Ryan Jones received a yellow card for cynically slowing the ball down.
Although they failed to take advantage of the extra man, as the half finished 0-0, the Dragons opened the scoring in the second period when good hands from Tyler Morgan and Cory Hill sent Rees over.
That try seemed to spark the contest and just six minutes later Nic Cudd was sin-binned for blocking Biggar and the stand-off kicked the resultant penalty to reduce the deficit to 7-3.
Cudd's absence then saw the Ospreys touch down for the first time in the encounter as the Dragons finally cracked under pressure and Habberfield crossed the whitewash from close range.
But the Dragons refused to lie down and Prydie levelled matters following Jonathan Spratt's yellow card for a deliberate knock-on.
However, the scrum, which had proven such a good weapon for Tandy's side throughout, was decisive as the forward eight won a penalty which their stand-off converted to give them the lead.
A late penalty try for yet another dominant set-piece then rubberstamped the win for the Ospreys as they retained their play-off hopes.
Yellow Cards: Cudd, Morgan
Tries: Habberfield, Penalty Try
Cons: Biggar 2
Pens: Biggar 2
Yellow Cards: R Jones, Spratt
Dragons: 15 Hallam Amos, 14 Tom Prydie, 13 Pat Leach, 12 Jack Dixon, 11 Will Harries, 10 Kris Burton, 9 Richie Rees, 8 Taulupe Faletau, 7 Lewis Evans, 6 Netani Talei, 5 Matthew Screech, 4 Andrew Coombs (c), 3 Duncan Bell, 2 T. Rhys Thomas, 1 Phil Price
Replacements: 16 Sam Parry, 17 Owen Evans, 18 Bruce Douglas, 19 Cory Hill, 20 Nic Cudd, 21 Jonathan Evans, 22 Jason Tovey, 23 Tyler Morgan
Ospreys: 15 Richard Fussell, 14 Jeff Hassler, 13 Jonathan Spratt, 12 Ashley Beck, 11 Hanno Dirksen, 10 Dan Biggar, 9 Tom Habberfield, 8 Dan Baker, 7 Justin Tipuric, 6 Joe Bearman, 5 Alun Wyn Jones (c), 4 Ryan Jones, 3 Aaron Jarvis, 2 Scott Baldwin, 1 Duncan Jones
Replacements: 16 Scott Otten, 17 Nicky Smith, 18 Adam Jones, 19 Tyler Ardron, 20 Sam Lewis, 21 Tito Tebaldi, 22 Sam Davies, 23 Aisea Natoga
Referee: Nigel Owens (Wal)
Assistant referees: Neil Hennessy, Jon Mason (both Wal)
TMO: Derek Bevan (Wal)