A Cardiff Blues blitz which brought 27 points in a devastating 20-minute spell helped the home side turn a half-time deficit into a festive bonus point victory over their near neighbours and rivals.

The Newport Gwent Dragons began the day as the leading Welsh region in the Magners League, with a mathematical chance of going top.

A 13-3 lead at the interval reflected their superiority over the lacklustre Blues, but whatever coach David Young said in the dressing room brought an incredible 39 points without reply as the Cardiff outfit thrilled the 15,210-strong crowd with their biggest win at the new Cardiff City Stadium.

Speaking after the game, Young said: "We were letting ourselves down in the first half, I thought the Dragons really wanted it a bit more than us.

"Any 50-50s they won and that's certainly what we said at half-time - we've got to match their enthusiasm and their attitude and our quality would take over.

"That's something that we had to go out and make happen and not expect it to happen."

The Blues were the first to threaten and after Ben Blair had struck a post with a penalty, the New Zealander succeeded with an easier effort to give the home side the lead.

It did not last though. Dragons full-back Jason Tovey was off target from a long range penalty, but his side were soon in front when winger Aled Brew popped up in midfield to capitalise on a quick turnover and race in at the corner.

Fly-half James Arlidge converted off an upright and extended the Dragons' lead with a penalty, but the Japanese international also missed two kickable chances - one for an offence at the breakdown which earned Blues hooker Rhys Thomas 10 minutes in the sin-bin.

The Blues had an opportunity to get back into the game as they pressurised the Dragons' line, but the backs were left without the ball as the forwards continued to get little reward from their close-in pick and drives.

That wastefulness was punished in the final seconds of the half when Tovey gathered an aimless clearance kick by Blues fly-half Sam Norton-Knight to drop a goal from 45 yards.

Incredibly, that turned out to be the Dragons' last score. The Blues went up several gears on the restart and within eight minutes they were ahead.

Scrum half Richie Rees, who turned in an excellent display, ran a penalty from deep in his own half and Blair claimed the points when the Dragons infringed again.

Then, a flowing move down the right ended with big lock Bradley Davies charging over. Blair converted and added a further penalty to level at 13-13.

A second Blues try soon followed. The Dragons' defence dithered beneath a high kick from Blair, the ball was allowed to bounce and cannoned to winger Richard Mustoe, who trotted in unopposed to give Blair a simple conversion.

The rampage continued when the lively Rees raced over from the base of a scrum, again without a hand laid on him as the shellshocked Dragons crumbled under the onslaught.

Their mood was not improved when try scorer Brew was yellow carded, and Tom Shanklin emphasised the amazing change of fortunes when he followed up his own kick ahead to go under the posts for the Blues' bonus point-clinching try. Blair again added the extras.

The final nail in the coffin came with a try in the left-hand corner by Tom James, who had had an earlier effort ruled out for a dropped ball. Blair missed the conversion, but that was of little consolation to the well-beaten Dragons.