Corey Domachowski proved the unlikely match-winner after snatching a dramatic last-gasp victory at Rodney Parade.

Harrison Keddie had followed Rio Dyer over the try line as Dragons came back in the second half of a niggly derby.

But replacement prop Domachowski barged over 30 seconds from time, after two from Tomos Williams either side of Josh Adams' try, to sneak a thrilling win.

Dragons were honest and gutsy with their display but that will not soften the blow of this loss.

They had a win of genuine meaning in their hands but the knack of winning - and losing - told in the end as Cardiff were rewarded for being bold and clinical.

Evans kicked a penalty half the length of the field to set up an attacking lineout five metres out from which the big prop drove over.

Under Gatland's gaze

Scrum-half Williams was outstanding, as was back rwo Taulupe Faletau, as Cardiff climbed to fifth in the United Rugby Championship.

And they will enjoy these local bragging rights in front of new Wales coach Warren Gatland, returning to the role.

Wales hopefuls Evans, Thomas Young, Rhys Carre and Dragons wing Ashton Hewitt will all have given Gatland food for thought.

However, back Adams will be a worry after limping off injured and Dragons lock Will Rowlands confirmed before kick-off he will miss the Six Nations.

Flanker Young gave another intelligent display, Carre scrummaged and carried well to set up a try, while Evans replaced Rhys Priestland at 10 to set up three more tries.

Cardiff's finishing was the difference as they led 14-11 at half-time against the run of play with two tries in three minutes.

Dragons dominated the opening exchanges but failed to capitalise.

Wing Hewitt was full of running, twice beating Owen Lane on the left touchline as well as Adams, who was switched from wing to full-back with Liam Williams still a week from a return.

A feisty clash started with Bradley Roberts, in his first Boxing Day derby, shown a yellow card for a petulant trip off the ball.

Dragons still managed to take a six-point lead through the boot of Hanrahan.

Ross Moriarty had a point to prove after missing the autumn Test series and was in the thick of the action both on and off the ball.

However, his opposite number and Wales rival Faletau was another class.

The number eight popped up seemingly everywhere as Cardiff finally got their attack going after 33 minutes.

Prop Carre, another looking to rekindle his Test ambitions, was also twice involved, handing Williams the scoring pass with a well-timed off-load.

Priestland limped off with an ankle injury but replacement Evans immediately kicked the conversion and was soon adding another after setting up a second try within a minute.

His deft inside pass to Lane opened space outside for Adams to touch down for a 14-6 lead.

Dragons were reeling but hit back before half-time. Moriarty carried and Steff Hughes' lofted pass that was finished by Dyer out wide.

Cardiff responded on 51 minutes, Evans' quick catch-and-pass opened space for Adams whose delightful no-look left-foot kick put Williams in for a second.

Adams went off with a knee injury minutes later and Dragons slowly wrestled back momentum.

Hewitt's kick-chase won a penalty and a well-worked Dragons lineout caught Cardiff napping and captain Keddie finished the drive.

Hanrahan converted and added a 71st-minute penalty for a 22-21 lead only for Evans to set up Cardiff's late, late winner.

Dragons head coach Dai Flanagan:

"It's a lot about belief with our team. We have some really good players and a lot of tough guys but they just need to believe more that they are that good.

"We dominated about 60 to 70 per cent of that game but there were a few areas we should have controlled better and 14 points before half-time killed us. It left us with so much to do.

"This obviously hurts and we need to start winning these games and I'm convinced that we will if we start believing how good we can be."

Cardiff head coach Dai Young:

"It was a tough, physical game and this is a tough place to play so we are thrilled to go home from a real ding-dong Welsh derby with five points.

"It came down to perseverance right at the end. It looked a bit of a mountain but we got a great turnover, a fantastic kick from Jarrod and then we managed to get over.

"There were a lot of big performances from some of our top players and that's what you expect from them. They can do things that change games."

Dragons: Angus O'Brien; Rio Dyer, Steff Hughes, Jack Dixon, Ashton Hewitt; JJ Hanrahan, Rhodri Williams; Rhodri Jones, Bradley Roberts, Chris Coleman, Joe Davies, George Nott, Aaron Wainwright, Harri Keddie (capt), Ross Moriarty.

Replacements: Brodie Coghlan, Aki Seiuli, Lloyd Fairbrother, Matthew Screech, Sean Lonsdale, Lewis Jones, Sam Davies, Sio Tomkinson.

Cardiff: Josh Adams; Owen Lane, Rey Lee-Lo, Ben Thomas, Theo Cabango; Rhys Priestland, Tomos Williams; Rhys Carre, Liam Belcher, Dmitri Arhip, Lopeti Timani, Rory Thornton, Josh Turnbull (capt), Thomas Young, Taulupe Faletau.

Replacements: Kirby Myhill, Corey Domachowski, Will Davies-King, Seb Davies, Ellis Jenkins, Lloyd Williams, Jarrod Evans, Mason Grady.

Referee: Ben Whitehouse (WRU)

Assistant referees: Mike English (WRU), Aled Evans (WRU)

TMO: Sean Brickell (WRU)