The visitors started the brighter at the Cardiff City Stadium, taking the game to Blues during the opening exchanges and Matthew Jones opened the scoring with a straight forward penalty.
Casey Laulala was stretched off early on for the home side. The centre picked up a head injury in a midfield collision and received lengthy treatment on the field.
Ben Blair kicked a penalty for the Blues to cancel out Jones' earlier effort before former Dragons fly half Ceri Sweeney started a flowing move from inside his own half that led to Wales winger, Leigh Halfpenny scoring the first try of the evening. Blair converted and brought up his 1000thpoint for the region.
Thomas scored the first of his tries as he finished off a sweeping move which had Sweeney at the helm once again and Blair converted to put the home side 11 points clear.
Cardiff dominated possession and territory and the Dragons had just two penalties from Jones to show for the first half as they went into the break 20-6 down.
The Dragons got the score they desperately needed, striking first in the second half. Jones created space for Tom Riley to race clear from their own twenty-two, who then offloaded to Will Harries and the full-back danced along the touchline to score. Jones converted from out wide.
Blair kicked his fourth penalty of the evening and then Thomas went over for his second try mid-way through the second half, powering his way to the line.
Blues talisman Xavier Rush claimed the bonus to the delight of the 11,000 strong crowd as the New Zealander crashed his way over the line, dragging two defenders along with him. Blair converted and added another penalty as he made it nine from nine with the boot.
The Dragons claimed a late consolation as replacement Adam Hughes sprinted clear to score on the stroke of full time.
CARDIFF BLUES: B Blair; L Halfpenny, C Laulala (D Hewitt, 6), T Shanklin, C Czekaj; C Sweeney, L Williams; G Jenkins, T R Thomas (Williams 73), S Andrews (Yapp 53); B Davies, P Tito, capt; M Molitka (Paterson, 48), X Rush, M Williams. Subs: R Williams, T Filise, J Yapp, D Jones, M Paterson, R Rees, D Parks, D Hewitt.
Scores: Tries Halfpenny, Thomas (2), Rush. Cons, Blair (4). Pens, Blair (5).
NEWPORT GWENT DRAGONS: W Harries; M Pewtner (Hughes, 48), T Riley, R Gomer-Davies, A Brew; M Jones (Connor, 72), W Evans (Griffiths, 72); H Gustafson, S Jones (Burns, 62), B Castle (Hall, 60); L Charteris, capt, R Sidoli (Morgan 54); D Lydiate (Coombs, 70), G Thomas, R Sowden-Taylor. Subs: L Burns, N Hall, A Coundley, S Morgan, A Coombs, A Hughes, N Griffiths, S Connor.
Scores: Tries, Harries, Hughes. Cons, Jones. Pens, Jones (3).
Yellow Card: Ben Castle.
Referee:N Owens (Wales)