Cardiff Blues moved up to third in the Magners League standings on Friday after they edged out neighbours the Ospreys 27-25 at Cardiff City Stadium.
Tries from Tom James and Richard Mustoe put Cardiff in control, and they led 24-3 early in the second half, but Ospreys fought back to make it a close finish.
The Blues started brightly, hoping to take advantage of the fact that for the bulk of the Ospreys side it was their second game in four days while the Blues had their scheduled game against the Dragons called off.
Cardiff earned a penalty straight from the kick-off which outside-half Dan Parks comfortably kicked from 25 yards. He added another penalty in the fourth minute, once again coming from a ruck infringement by the visitors.
The Blues were dominating territory and were happy to keep passing the ball in tight spaces, an ambition which earned reward when left wing James went over on the left with full-back Chris Czekaj giving the scoring pass following a break up the right by Casey Laulala.
Parks missed the conversion from wide out, while Ospreys outside-half Dan Biggar got his side on the scoreboard with a 45-yard penalty from a scrum. He would go on to miss two more long-range efforts in the first half.
Parks put more points on the board to reward Cardiff's pressure as he slotted two drop goals to extend the lead to 17-3 at half-time.
Ospreys needed to make something happen in the second half, but instead it was the Blues who extended their lead in the early stages following the sin-binning of props Paul James and Taufa'ao Filise.
Wing Mustoe injected a burst of pace and ran through unopposed for a try from 40 metres out. Parks converted.
Belatedly Ospreys were stung into action and a lengthy period of attack in the Blues 22 eventually brought a reward when prop Paul James forced his way over from short range after 59 minutes.
Ospreys were given further hope when wing Tommy Bowe snatched an interception and went 50 yards for the try which was converted by James Hook.
Ospreys then narrowed the points difference to within a score when Hook added another penalty, with both sides having substituted their starting outside-halves.
Ceri Sweeney landed a penalty at the other end to give the Blues extra breathing space.
And although centre Andrew Bishop scored a late try for Ospreys, converted by Hook, it was only enough to earn a losing bonus point.
For Cardiff Blues:
Tries: James, Mustoe
Pen: Parks 2, Sweeney
Tries: James, Bowe, Bishop
Con: Hook 2
Pen: Biggar, Hook
Cardiff Blues: 15 Chris Czekaj, 14 Richard Mustoe, 13 Casey Laulala, 12 Jamie Roberts, 11 Tom James, 10 Dan Parks, 9 Richie Rees, 8 Maama Molitika, 7 Sam Warburton, 6 Andries Pretorius, 5 Paul Tito (capt), 4 Bradley Davies, 3 Tafa'ao Filise, 2 T Rhys Thomas, 1 Gethin Jenkins.
Replacements: 16 Rhys Williams, 17 John Yapp, 18 Sam Hobbs, 19 Deiniol Jones, 20 Martyn Williams, 21 Tom Slater, 22 Ceri Sweeney, 23 Leigh Halfpenny.
Ospreys: 15 Barry Davies, 14 Tommy Bowe, 13 Andrew Bishop, 12 James Hook, 11 Richard Fussell, 10 Dan Biggar, 9 Jamie Nutbrown, 8 Jonathan Thomas, 7 Marty Holah, 6 Jerry Collins, 5 Alun Wyn Jones (capt), 4 Ian Gough, 3 Adam Jones, 2 Richard Hibbard, 1 Paul James.
Replacements: 16 Huw Bennett 17 Ryan Bevington, 18 Craig Mitchell 19 Ian Evans, 20 Ryan Jones, 21 Mike Phillips, 22 Sonny Parker, 23 Nikki Walker.
Referee: Nigel Owens (Wales)
Assistant referees: Gwyn Morris (Wales), Sean Brickell (Wales)
Television match official: Tony Rowlands (Wales)