Three tries in the final 20 minutes from the Ospreys' dominant forward pack were enough to see off the Blues at the Cardiff City Stadium. Alun Wyn Jones, Adam Jones and Tom Smith touched down for the visitors, who scored 27 unanswered points in the second half.
With two league games left to play, the result leaves the Ospreys favourites to secure second place in the RaboDirect PRO12 table, and so guarantee a home tie in the play-offs. For the Blues, seventh in the table, a miserable run of form shows no few signs of coming to an end.
Leigh Halfpenny and Dan Biggar traded early penalties. The Blues full-back added two more towards the end of a scrappy first-half, and they went in at the break 12-6 ahead.
The Ospreys' superiority up front began to tell, though. After a period of pressure in the the home side's 22 early in the second half, Blues Number 10 Ceri Sweeney was harshly yellow-carded for a deliberate knock-on. The visitors made that advantage count, scoring 13 points while he was off the pitch. Biggar first kicked two penalties to level the scores, before Ospreys captain Alun Wyn Jones cantered through some tentative tackling, and reached out to score. Biggar converted.
His Wales international colleague Adam Jones extended the Swansea side's lead. The prop picked the ball up from a ruck and drove over the line, with Blues scrum half Lloyd Williams able to do no more than hang on for the ride. Again, Biggar kicked the extras.
The dominance of the Ospreys pack was then full rewarded with a real forwards' try in the closing minutes. Replacement Number 8 Tom Smith touched the ball down after the Blues were shoved back over their own line from a scrum. Biggar slotted an easy conversion.