A stuttering home first half performance saw under-par Blues trail by ten points as host of mistakes proved costly with a try from visiting hooker Elliot Dee and the accurate boot of Tom Prydie putting Dragons into a comfortable lead.
The lead grew even further in the opening stages of the second half with a penalty try from the Dragons before Blues finally clicked into gear in the final quarter.
Lock Jarrad Hoeata and replacement scrum half Tavis Knoyle scored two tries in five minutes to spark home hopes of a thrilling turnaround.
But the fired-up Dragons were not to be denied deserved derby day spoils as they held out in torrential rain to claim victory in the first part of a double header between the teams.
Mark Hammett and his team now have six days to re-group before the teams lock horns again at Rodney Parade on New Year’s Day.
Blues had been simply inspired seven days earlier in the first half against Scarlets. But this opening 40 minutes was forgettable for the home side for all the wrong reasons as they failed to ignite in fiery derby day conditions and roared on by a crowd of 10,900.
Fly half Gareth Davies saw an early penalty attempt slip wide right and Blues looked to open up and play in the opening exchanges with wide men Alex Cuthbert and Lucas Amorosino prominent.
But handling errors in the rain and a lively Dragons display always kept the home side on their toes with Jason Tovey missing a snap drop goal attempt before Prydie did put them ahead after a breathless opening quarter.
Centre Gavin Evans made the first home line break of the game, but could not find support runners. And Dragons hit back as they also broke into space, after a loose pass fell kindly, and Tovey’s grubber in behind forced Ellis Jenkins to carry the ball over and concede a five-metre scrum.
The visitors repeatedly looked to smash over from close range, with scrum half Jonathan Evans darting down the shortside, before tempers flared off the ball and a penalty against Rynard Landman handed Blues a much-needed reprieve.
A penalty for obstruction, from a huge high kick from full back Joaquin Tuculet, gave Davies a second kickable attempt of the game, but he was narrowly off target as his kick fell wide left in the wind.
Visiting wing Hallam Amos – just hours after news that he had signed a NDC – was proving a menace for Blues as he stepped inside tackles and had alarm bells ringing.
Pressure was mounting from the visitors and when a penalty at scrum time saw Tovey kick for the corner and not the posts the Dragons looked to turn up the heat. The decision paid dividends as the driving lineout crashed over with Dee touching down for a 10-0 lead.
More danger soon followed as Dragons this time broke from deep inside their own 22 and put the ball quickly through hands for Tovey to kick in behind and allow Amos to bundle Tuculet into touch.
Prydie then saw a drop goal charged down, but the penalty was already secured and the full back did the rest as a 13-0 lead was nailed down with four minutes until the break.
Blues only response came deep into injury time as Davies slotted a penalty from a central position, after a scrum infringement, as Dragons left the field with a ten-point lead.
More Dragons pressure at the start of the second half forced Blues to repeatedly play from deep and Hammett started to unload his bench in the hunt for a spark, with Gareth Anscombe among those to enter the fray.
However, within seconds of the changes being made, the visitors went even further ahead as a massive driving lineout saw the march down field and power towards the whitewash. When the drive was dragged down, referee Hodges had little hesitation in awarding a penalty try.
Blues were visibly straining for a breakthrough as they introduced more fresh faces in the quest for a foothold as the rain continued to lash down. And when they did go wide left at pace, a slippery offload from Tuculet failed to find Evans on his shoulder.
The home forwards did come alive in the final 20 minutes and a series of powerful drives, led by the determined Josh Navidi, Lou Reed and Kristian Dacey, saw them rumble up close.
When the ball was freed, Anscombe found a gap to split the defence and New Zealand ace Hoeata crashed in from close range to cut the lead back to 20-10.
Minutes later it got even better as the forwards once again drove on in numbers before, when the ball was spun wide, Anscombe again stepped inside a tackle and the alert Knoyle picked up to stretch over and dot down. Suddenly, from nowhere, it was game on.
Dragons, though, were not to be ruffled and a simple penalty kick from Prydie settled any nerves before a breathless final five minutes unfolded.
Blues looked to play from deep inside their 22 and when Cuthbert brushed off tackles his inside pass just failed to find a flying Anscombe on his shoulder.
Back came Dragons and, with play suddenly broken up, replacement fly half Dorian Jones showed his raw pace to race down the left touchline and score. But, in dramatic scenes, the try was then chalked off for a knock-on in the build-up by the TMO and Blues had one last chance.
Dragons looked to run the clock down only to cough up ball. With one last attack, Cuthbert again broke tackles from deep and made halfway, but when the ball was flipped wide it drifted forward and the fight-back had fallen just short.
17m Prydie p 0-3
32m Dee t Prydie c 0-10
37m Prydie p 0-13
40m Davies p 3-13
47m Penalty t Prydie c 3-20
64m Hoeata t Anscombe c 10-20
69m Knoyle t Anscombe c 17-20
74m Prydie p 17-23
Cardiff Blues: 15 Joaquin Tuculet, 14 Alex Cuthbert, 13 Cory Allen, 12 Gavin Evans, 11 Lucas Amorosino, 10 Gareth Davies (Anscombe 46), 9 Lewis Jones (Knoyle 57), 1 Sam Hobbs (Jenkins 51), 2 Matthew Rees (Dacey 51), 3 Adam Jones (Filise 46), 4 Jarrad Hoeata, 5 Lou Reed (Cook 66), 6 Josh Turnbull, 7 Ellis Jenkins (Vosawai 57), 8 Josh Navidi
Replacements: 16 Kristian Dacey, 17 Gethin Jenkins, 18 Taufa’ao Filise, 19 Macauley Cook, 20 Manoa Vosawai, 21 Tavis Knoyle, 22 Gareth Anscombe, 23 Adam Thomas