Teenage fly-half Rhys Patchell starred on his first Pro12 start as Cardiff Blues edged a low-key Welsh derby.
The 19-year-old kicked three penalties and converted Alex Cuthbert's second-half try in a composed display.
Newport Gwent Dragons led 5-3 at the break after Steffan Jones finished off a rare attacking platform.
But they failed to build on their advantage as handling errors littered their play, and conceded Cuthbert's try when the visitors were down to 14 men.
The derby struggled to ignite despite perfect conditions at Rodney Parade, with any hope of forward momentum thwarted as both sides fell foul at the tackle area.
They were also guilty of missing scoring opportunities as Tom Prydie and Jones missed penalties at goal for the home side, and Patchell wide with his first attempt for the Blues.
But the young fly-half grew in stature and only a marginal forward pass call prevented him from marking his first start by creating an opening try for Gavin Evans.
A superb covering tackle by Prydie on Cuthbert then denied the visitors once more, but Patchell's first penalty rewarded their efforts.
The Dragons responded immediately with Jones's try, set up by a typically dynamic run by Toby Faletau.
For once, the home side secured quick ball from a succession of rucks, and Jones stepped off his right foot to beat the stretched defence to score.
Prydie missed the straightforward conversion, leaving the Dragons with a slender half-time lead.
Prop Phil Price was held up inches short as the Dragons pressed after the break, with opposite number Nathan Trevett sent to the sin bin for an offence moments earlier.
But despite the numerical disadvantage, the Blues pounced on a Dragons mistake to score.
Centre Evans was awake to the opportunity and managed to get his pass away to Cuthbert, who raced home unopposed. Patchell converted.
The try came a minute after Jamie Roberts came off the replacements' bench for his first appearance since March after knee surgery.
But the Blues failed to make his presence felt as the mistakes continued, but Patchell held his nerve to land two penalties in the final four minutes to seal the region's first win at Rodney Parade since 2010.
Newport Gwent Dragons: Dan Evans, Will Harries , Pat Leach, Andy Tuilagi, Tom Prydie; Steffan Jones, Jonathan Evans; Phil Price, Steve Jones, Dan Way, Ian Nimmo, Adam Jones, Dan Lydiate, Lewis Evans (capt), Toby Faletau.
Replacements: Hugh Gustafson, Aaron Coundley, Nathan Buck, Jevon Groves, Tom Brown, Liam Davies, Ashley Smith, Adam Hughes.
Cardiff Blues: Thomas Williams; Alex Cuthbert, Gavin Evans, Dafydd Hewitt, Harry Robinson; Rhys Patchell, Lloyd Williams; Nathan Trevett, Marc Breeze, Taufa'ao Filise, Bradley Davies, James Down, Josh Navidi, Sam Warburton, Andries Pretorius (capt).
Replacments: Kristian Dacey, Thomas Davies, Benoit Bourrust, Lou Reed, Rory Watts-Jones, Lewis Jones, Ceri Sweeney, Jamie Roberts.
Referee: Neil Hennessy (WRU)
Assistant Referees: James Jones, Wayne Davies (both WRU)
Citing Commissioner: John Charles (WRU)
TMO: Gareth Simmonds (WRU)