Blues fly-half Lee Thomas opened the scoring with a well-struck penalty goal and doubled the score with a second goal after Gloucester flanker James Forrester was sin-binned for a professional foul in front of his uprights. It was a deserved lead, but it lasted barely 60 seconds.
Quick ball to flying winger Marcel Garvey, a weak "tackle" from opposite number Craig Morgan and a superb sideline conversion from Paul gave 14-man Gloucester the lead. The Blues had a royal chance to hit back, but criminally ignored a four-man overlap on the right-hand side and went into the halftime break trailing 6-7.
A tackle-busting run from former Cardiff prop Gary Powell set up the first try of the second half, with referee Lewis ignoring a possible crossing incident in the Gloucester midfield and fullback Jon Goodridge snapping up a clever Duncan McRae chip to score. Thomas butchered a chance to narrow the margin with a penalty miss from a handy range, but made amends from a wider angle a moment later.
Paul gave his side a 20-9 lead with two penalty goals in as many minutes just after the hour mark, and Gloucester looked to have sealed the match when Goodridge sneaked over in the corner. But referee Lewis incurred the wrath of the visiting fans when he disallowed the try and sin-binned Powell for punching.
The call unsurprisingly angered the Gloucester players and the next breakdown erupted into an all-in brawl, with Blues lock Deiniol Jones becoming the next player to be shown a yellow card. Paul, who was extremely lucky to still be on the field after his role in the fight, converted the penalty goal amid jeers echoing around a furious Arms Park.
Morgan dived over in the corner to narrow the margin to 23-14, and Thomas' nerveless sideline conversion in front of booing Gloucester fans made it a seven-point ballgame with five minutes left on the clock. A McRae dropped-goal attempt missed by inches, and Gloucester clung to their lead until the final whistle.
Cardiff Blues 16 Gloucester 23
HT: 6-7 Attendance: 10,186
Cardiff Blues: R Williams (N MacLeod 72); F Tuilagi, S James, T Shanklin, C Morgan; L Thomas, R Powell; G Jenkins, R Thomas, M Jones (J Yapp 54), D Jones, R Sidoli, N Thomas (R Sowden-Taylor 65), M Williams (capt), K Schubert
Scorers: Try - C Morgan; Con - L Thomas; Pens - L Thomas (3);
Yellow cards: D Jones (70)
Gloucester: J Goodridge; M Garvey, T Fanolua (N Mauger 62), H Paul, J Bailey; D McRae, A Gomarsall; C Bezuidenhout, J Parkes, G Powell, A Eustace, M Cornwell (A Brown 44), J Forrester (P Buxton 74), J Boer (capt), A Balding
Scorers: Tries - M Garvey, J Goodridge; Cons - H Paul (2); Pens - H Paul (3);
Yellow cards: J Forrester (31), G Powell (70)
Man of the match: A Balding (Gloucester)
Match points: Cardiff Blues 1 pts; Gloucester 4 pts
Referee: Alan Lewis (Ireland)