|Pro14 Rainbow Cup:|
|Cardiff Blues (10) 17|
|Tries: Adams, T Williams Cons: B Thomas, J Evans Pens: B Thomas|
|Dragons (3) 16|
|Try: Lawrence Cons: S Davies Pen: S Davies 3|
Wales back Owen Lane and Dragons hooker Rhys Lawrence were shown red cards as Cardiff Blues clinched victory in the Pro14 Rainbow Cup.
Lane was guilty of a shoulder to the head of Argentina scrum-half Gonzalo Bertanou and Lawrence was sent off for a similar offence on Josh Turnbull.
Josh Adams, named in the Lions squad on Thursday, and Teddy Williams crossed for Cardiff while Lawrence had earlier scored Dragons' only try.
Sam Davies kicked 11 Dragons points.
The visiting fly-half missed a late long-range penalty to win a game that was influenced by the new trials laws in the Rainbow Cup.
Lane was dismissed after 46 minutes but Blues were able to replace him with another player for the final 14 minutes and that proved pivotal.
Adams returned as one of nine changes from the side defeated by Ospreys two weeks ago and opened the scoring following a flowing move with the assist from Ben Thomas, who also converted.
Dragons had started slowly after making seven changes from their 52-32 opening-round win against the Scarlets with centre Jamie Roberts picked to play against his former side.
Wales flanker Ross Moriarty led Dragons for the first time while full-back Ioan Davies, on loan from Cardiff Blues, made his first appearance for Dragons against his parent club.
Dragons second-row Matthew Screech, who is set to join Blues next season, was forced off early to be replaced by Ben Carter.
Blues number eight Sam Moore, who was making his return from injury, was given a warning by Scottish referee Mike Adamson for early persistent offending.
Sam Davies missed a penalty before Thomas slotted over three points to extend the lead to 10 points.
Dragons responded with flanker Taine Basham prominent as Davies slotted over their first points with the final kick of the half.
Moriarty activated one of the new law trials with a captain's challenge as he claimed Cory Hill had taken Basham off the ball with an illegal shoulder charge, but it was dismissed.
Lane's needless shoulder to the head of Bertranou resulted in a red card after numerous replays and Dragons responded with a try for replacement Lawrence.
Davies converted to level the scores before slotting a penalty to give Dragons the lead for the first time.
Adams received treatment on a neck injury before fellow Blues wing Jason Harries was yellow carded for a deliberate knock-on as the hosts were reduced to 13 men.
Dragons missed try-scoring chances with the hosts' scramble defence impressive, typified by Turnbull producing one terrific turnover in particular that changed the game. Dean Ryan's side had to be content with a third Davies penalty.
Another law trial was activated 20 minutes after Lane's dismissal, with Blues allowed to replace their sent-off centre and Ben Thomas returning to the field.
Harris returned to ensure the home side had a full complement, with replacement lock Williams crashing over just after he came on for the decisive score.
Blues skipper Turnbull immediately enacted his captain's challenge after he was the victim of a shoulder to the head from Lawrence with the Dragons front-rower shown a red card.
Jarrod Evans popped over the conversion to give Blues a one-point lead before Davies' late long-range effort went wide and the hosts celebrated victory.
- Watch Scrum V Pro14 Rainbow Cup highlights on BBC Two Wales from 19:15 BST on Sunday, 9 May and later on demand.
Cardiff Blues director of rugby Dai Young: "You have to be pleased with the character and it was certainly a game of two halves. The first 35 minutes, I thought we were excellent but going into half-time I was disappointed we didn't have a bigger lead.
"We bombed one of two tries, there were some kicking inaccuracies and I felt the only way the Dragons were in the game was through our inaccuracies and a little bit of poor discipline."
Dragons director of rugby Dean Ryan: "We had numbers on them and should have taken more opportunities
"It was a very different challenge today. In the first half we were getting tripped up at the breakdown and in the set piece.
"We wanted to play faster and quicker and see what impact it had. For the half-hour after the break we created lots and they didn't know how to cope with us.
"We gain a lot from that, we are just disappointed we didn't put the result away."
Cardiff Blues: Hallam Amos; Jason Harries, Owen Lane, Max Llewellyn, Josh Adams; Ben Thomas, Jamie Hill; Rhys Carre, Kirby Myhill (capt), Dillon Lewis, Seb Davies, Cory Hill, Josh Turnbull, Olly Robinson, Sam Moore.
Replacements: Kristian Dacey, Brad Thyer, Will Davies-King, Teddy Williams, James Ratti, Ellis Bevan, Jarrod Evans, Willis Halaholo.
Dragons: Ioan Davies; Jonah Holmes, Aneurin Owen, Jamie Roberts, Rio Dyer; Sam Davies, Gonzalo Bertranou; Josh Reynolds, Taylor Davies, Leon Brown, Joe Davies, Matthew Screech, Ross Moriarty (c), Taine Basham, Aaron Wainwright
Replacements: Rhys Lawrence, Greg Bateman, Chris Coleman, Ben Carter, Harrison Keddie, Dan Babos, Josh Lewis, Jack Dixon.
Referee: Mike Adamson (SRU)
Assistant referees: Dan Jones, Mike English (both WRU)
TMO: Sean Brickell (WRU)
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