Josh Turnbull was the hero for Cardiff Blues with a late try to secure derby bragging rights against the Dragons at Rodney Parade.
The Wales forward went over from close range in the 67th minute, with Jarrod Evans converting for a 13-12 win in the Guinness PRO14 clash in Newport.
It capped a strong second-half performance by the Blues after they had trailed 9-3 at the break courtesy of three penalties by Dragons fly-half Josh Lewis to one by opposite number Evans.
The home side were hunting a first PRO14 win against their fiercest enemy since 2014 but came up short after spending almost all of the second half pinned inside their own territory.
They could have no complaints about an 11th successive championship loss to the men from the capital in a poor-quality clash in torrential rain.
The Dragons made a bright start and led 9-0 after 18 minutes thanks to fly-half Lewis punishing Blues indiscipline with three nice strikes in challenging conditions.
It took superb defence by Tavis Knoyle for the home side to retain their lead, with the scrum-half ripping the ball away from hooker Kristian Dacey on the line.
The Blues had enjoyed a period of pressure but were stopped from making that show on the scoreboard by errors in the 22.
They had been going for the corner with penalties but that changed on 32 minutes when Evans opened his account to make it 9-3.
That’s how it stayed at half-time, with the visitors happy to kick the ball out, confident that they would be able to turn the screw with the wind at their backs.
However, it was the Dragons that struck first, with Lewis punishing an offside six minutes after the resumption to make it 12-3, reaping the rewards of good ball retention when carrying hard.
The Blues went to the corner with a penalty and came within a yard of the line only to then knock on when playing with advantage, leading Evans to settle for splitting the posts to make it 12-6 after 54 minutes.
They were within a score and turned it into a good decision when they opted for the corner in the 67th minute.
The Blues claimed the line-out and then inched to the line with pick and drives before Turnbull got over, Evans’ conversion making it 13-12.
The visitors ended the game hunting a clincher but were denied from a driving line-out, ensuring the Dragons at least had the consolation of a losing bonus point.
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