|Ospreys (27) 46|
|Tries: Jones, Walker 2, Arhip, John, Evans, Matavesi Cons: Davies 3, Biggar Pen: Davies|
|Cardiff Blues (10) 24|
|Tries: Dacey, James, Lee-Lo Cons: Anscombe 3 Pen: Anscombe|
Clinical Ospreys hammered Cardiff Blues in the first Welsh derby of the season.
Blues started well and led 10-3 after Kristian Dacey's try, but shipped 19 points after full-back Dan Fish was yellow carded for a professional foul.
Two tries by Eli Walker and scores by Alun Wyn Jones and Dmitri Arhip secured a bonus point before half-time.
Further tries by Ben John, Dan Evans and Josh Matavesi hammered home Ospreys' dominance, with Tom James and Rey Lee-Lo replying for Blues.
The result lifts the Swansea-based side into second place in the Pro12 table behind Ulster - who lost to Connacht - and overtaking the Blues, who suffered their second defeat of the season, in the process.
Ospreys coach Steve Tandy created the biggest headlines in the build-up to the game when he selected Sam Davies at fly-half ahead of Wales number 10 Dan Biggar.
And the 23-year-old stand-off rewarded his coach's faith with an assured performance before giving way to Biggar on the hour.
But his task was made easier by the dominance of the home pack after they saw-off Blues' energetic opening.
The match also saw the return to action of Ospreys flanker Dan Lydiate, who came off the bench for his first game since 29 May, when he was injured captaining Wales against England.
But wing Jeff Hassler was taken off the field on a stretcher with an ankle injury, and Wales scrum-half Rhys Webb limped off late in the game.
Blues, so impressive in winning their opening four games of the season, were ruthlessly punished whenever they made mistakes.
They were in the driving seat when Fish had a clearance kick charged down by Davies, and the full-back compounded the error when he pulled back the fly-half.
Referee Nigel Owens produced a yellow card and by the time Fish returned to the action Ospreys had scored three tries and were leading 22-10.
Moldova prop Arhip's try secured a bonus point before half-time and any hopes of a second-half fight back were extinguished when John scored 26 seconds after the interval after Blues made a hash of the re-start.
Evans' try was reward for another fine attacking display, while man-of-the-match, Ospreys flanker James King, had a serious rival for that honour in the shape of his captain and second row Jones.
Ospreys: Dan Evans; Jeff Hassler, Ben John, Josh Matavesi, Eli Walker; Sam Davies, Rhys Webb; Nicky Smith, Sam Parry, Dmitri Arhip, Bradley Davies, Alun Wyn Jones (Capt), James King, Justin Tipuric, Dan Baker.
Replacements: Scott Baldwin, Paul James, Ma'afu Fia, Rory Thornton, Dan Lydiate, Tom Habberfield, Dan Biggar, Ashley Beck
Cardiff Blues: Dan Fish; Blaine Scully, Garyn Smith, Rey Lee-Lo, Tom James; Gareth Anscombe, Lloyd Williams; Gethin Jenkins (capt), Kristian Dacey, Taufa'ao Filise, Macauley Cook, Josh Turnbull, Josh Navidi, Ellis Jenkins, Nick Williams
Replacements: Matthew Rees, Rhys Gill, Scott Andrews, James Down, Cam Dolan, Tomos Williams, Steven Shingler, Matthew Morgan
Referee: Nigel Owens (WRU)
Assistant Referees: Sean Brickell, Gareth Newman (WRU)
Citing Commissioner: Aurwell Morgan (WRU)
TMO: Tim Hayes (WRU)