Dragons suffered derby day heartbreak as a last-minute try saw Cardiff snatch a pulsating BKT United Rugby Championship clash at a sold-out Rodney Parade.
Wing Rio Dyer grabbed a first score, but Dragons found themselves behind at the break after visiting tries from Tomos Williams and Josh Adams.
Captain Harri Keddie blasted his way over to the cut the lead to a point with 15 frantic minutes to go before JJ Hanrahan kicked the Men of Gwent ahead.
But a cruel late twist saw replacement front row Corey Domachowski pile over in the dying seconds as the capital club took maximum points.
It was a painful result for Dragons – and second successive game that has been lost on the final play – as the team now switch attention to a New Year’s Day date in Llanelli.
Dragons made five changes for the clash with Angus O’Brien, George Nott, Steff Hughes, Ross Moriarty and JJ Hanrahan all called up.
An early cross field kick from Hanrahan found Hughes who himself kicked in behind, but the alert Adams just got to the loose ball before Ashton Hewitt.
Cardiff looked to spring an attack from deep with Adams and Thomas Young combing until the final pass was deemed forward as Taulupe Faletau dotted down.
A penalty at the lineout gave Rhys Priestland a first shot at goal, but the fly half pulled his kick wide of the target.
A scintillating break from Hewitt saw him scorch down the left flank and hand off Owen Lane, but a brilliant last-ditch tackle from Faletau saw the wing dragged into touch.
Hughes continued to show his game management skills with a clever kick in behind that Cardiff were forced to push into touch, but breakdown ace Young stole more ball in the shadow of the posts.
Dyer was the next to make a break as Dragons dominated territory in the opening 15 minutes.
Tempers flared off the ball after a kick downfield, with Roberts sent to the sin bin for a flick out at Young.
Stolen lineout ball, though, sprung another home attack and Hanrahan opened the scoring off the tee. A
n offside - after some aerial ping pong - resulted in another penalty and Hanrahan’s long-range effort crept over, as Roberts returned from the sin bin.
Cardiff hit back seven minutes before the interval as incessant pressure paid off with scrum half Tomos Williams the man to go over. Replacement Jarrod Evans added the extras.
The visitors struck again within two minutes as slick hands freed up space for Adams to dot down in the left corner.
Dragons needed a response and got it seconds before the interval as a floated wide pass from Hughes gave Dyer the room he needed to beat Cabango and Adams to the corner.
A pulsating opening to the second half saw Cardiff strike first as a penalty at scrum time marched Dragons back before Adams broke and his neat reverse grubber found Williams to score his second.
A cross field kick from Hanrahan found Aaron Wainwright but Cardiff swarmed to force a turnover, as front row replacements Aki Seiuli and Lloyd Fairbrother were introduced.
An offside penalty gave Dragons a chance to hit back and, after the driving maul was repelled, up stepped Hanrahan to add three.
Evans, though, added another kick of his own to nudge Cardiff further ahead at the hour mark.
A clever kick into wide open space from O’Brien forced Cabango to concede a penalty for holding on and Dragons immediately kicked to the corner.
The decision paid dividends as the forwards powered over with captain Keddie the man to find his way over the line. Hanrahan added the extras to cut the lead to a single point.
A superb touch finder from Hanrahan, as the game entered the final ten minutes, saw Rodney Parade in full voice and a penalty as the forwards drove on allowed the playmaker to put Dragons ahead.
But there was to be late twist as a penalty and resulting sublime touch finder from Evans set up the visitors for a final roll of the dice and Domachowski’s late intervention.
21m Hanrahan p 3-0
26m Hanrahan p 6-0
33m Williams t Evans c 6-7
36m Adams t Evans c 6-14
38m Dyer t 11-14
53m Williams t 11-19
58m Hanrahan p 14-19
61m Evans p 14-22
65m Keddie t Hanrahan c 21-22
72m Hanrahan p 24-22
79m Domachowski t Evans c 24-29
Dragons RFC: Angus O’Brien, Rio Dyer, Steff Hughes, Jack Dixon (Coghlan 20-36 (Tomkinson 61)), Ashton Hewitt, JJ Hanrahan, Rhodri Williams (Jones 75), Rhodri Jones (Seiuli 53), Bradley Roberts, Chris Coleman (Fairbrother 53), Joe Davies (Screech 67), George Nott, Aaron Wainwright, Harri Keddie (Lonsdale 72), Ross Moriarty
Replacements: Brodie Coghlan, Aki Seiuli, Lloyd Fairbrother, Matthew Screech, Sean Lonsdale, Lewis Jones, Sam Davies, Sio Tomkinson
Cardiff Rugby: Josh Adams, Owen Lane, Rey Lee-Lo, Ben Thomas, Theo Cabango, Rhys Priestland, Tomos Williams, Rhys Carré, Liam Belcher, Dmitri Arhip, Lopeti Timani, Rory Thornton, Josh Turnbull, Thomas Young, Taulupe Faletau
Replacements: Kristian Dacey, Corey Domachowski, Will Davies-King, Seb Davies, Ellis Jenkins, Lloyd Williams, Jarrod Evans, Mason Grady
Referee: Ben Whitehouse (WRU, 85th league game)