A penalty try and a Morgan Allen score put the Ospreys in pole position at the break, but they had to soak up extensive pressure in the third quarter after being reduced to 13 after yellow cards for Ian Evans and Cai Griffiths before a Hanno Dirksen touchdown rounded off the win.

It was the Blues who came racing out of the blocks, taking the lead inside three minutes through a Gavin Evans try in the corner. The home side secured quick ball from a lineout allowing them to move the ball through the phases, Tom Davies and Dafydd Hewitt both breaking the line before Wales cap Evans was able to reach over and ground in the corner, Joe Griffin successful with a difficult conversion attempt.

Matthew Morgan responded for the Ospreys within two minutes, a straightforward penalty from 20m out after a Blues tackler failed to roll away getting the visitors on the scoreboard.

Morgan was then able to reduce the deficit to just a point with another simple penalty from in front of the posts after Rhys Webb had showed great awareness at the base of a ruck, charging through the gap to carry 20m, Blues defenders going off their feet as they looked to secure the ball after Webb's progress had been halted.

A sharp Morgan break then took the Ospreys deep into Blues territory, his kick through giving his wing Dirksen something to chase, but it was Dan Fish who was first to the ball for the Blues at the expense of a scrum five.

The Ospreys had already appeared to have the upper hand in the setpiece, but it still came as something of a surprise when referee David Pearson indicated a penalty try as the white pack drove forward with the Blues scrum in disarray, without first resetting. Morgan's conversion took the score to 13-7 to the Ospreys with 20 played.

The Ospreys were on top at this stage, and just a couple of minutes later Morgan added another three points after Josh Navidi was guilty of coming in from the side.

Griffin had a chance to reduce the deficit but his penalty from a central position on the Ospreys 10m line just faded at the death.

Another strong Ospreys scrum on halfway gave them a platform to attack from, Rhys Webb and Justin Tipuric combining well before the skipper offloaded to Tom Prydie, who was hauled down just a couple of metres short by Gavin Evans.

They did score just 30 seconds later though, Morgan Allen, on as a blood replacement for Tom Smith, picking up at the base of another advancing Ospreys scrum to barge his way over for a try on his debut. The conversion was unsuccessful, leaving the score at 21-7.

Griffin was well short with a penalty effort from halfway after Tipuric was penalised at the breakdown.

A well-worked move then saw Kristian Phillips collecting the ball at pace near halfway, bursting through the Blues defence before chipping over the cover. A combination of Fish and Harry Robinson was able to get back and prevent the try, the TMO confirming a scrum to the Ospreys rather than the try.

Despite some sloppiness seeing the Ospreys lose ground at the scrum, they were still able to secure a penalty to allow Morgan to extend his side's lead with his fifth successful kick of the half.

Having opened the scoring, the Blues had a chance to round off the first forty, but Griffin was again off target with a difficult effort from close to the touchline to bring the opening period to a close.

HALF-TIME: CARDIFF BLUES 7 OSPREYS 24

Just as they had in the first half, the Blues started the second period on the offensive, camping themselves on the Ospreys line as they looked to find their way through some stubborn defence. The Ospreys were able to hold firm but only with the aid of a number of offences, which led to Ian Evans being shown yellow as Mr Pearson's patience wore thin.

As the Blues continued to apply pressure they remained unable to find a way through, a period of sustained pressure on the line once again ending with a yellow card, Griffiths joining Ian Evans in the bin as the Ospreys were reduced to 13. Incredibly, with a try seemingly the only outcome as the Blues pack looked to rumble forward against the Ospreys six man scrum, the ball squirmed out of the side allowing Webb to clear with the line still intact.

Dirksen then had to be alert to the danger as Gavin Evans looked to chip and chase up the right touchline, the youngster getting back to secure the ball behind the Ospreys line.

As the Blues looked to take full advantage of their extra numbers, last man Prydie did good defensive work to ankle tap James Loxton as he looked to sidestep on his way to the line, before getting straight back to his feet to haul down Steve Taylor. As the Blues recycled, Robinson looked to force his way over from close range, only for a combination of Webb and Prydie to force him into knocking on as he looked to ground it.

Despite the third quarter being played almost entirely inside the Ospreys 22, the visitors were able to survive their two yellow cards without conceding any points, much to the frustration of the Blues, and they almost caught their opponents out with a classic sucker punch. The Blues lost their own scrum on halfway, allowing Gareth Owen to put through a delightful kick to the corner that just bounced the wrong way as Phillips looked to collect for a simple score.

The next score went the Ospreys way, a series of pick and drives sucking in defenders as they edged their way forward, before the ball was spun wide to take advantage of the space near the touchline, Dai Flanagan's long pass releasing Dirksen who raced over to score. Flanagan missed the conversion, leaving it 29-7 at the finish.