Cardiff Blues fell to a disappointing derby defeat as the Ospreys flexed their forward muscle at the Cardiff City Stadium.
Following a slender victory over the Dragons on Boxing Day, the capital city outfit had been hoping to kick-off 2021 with a second successive Welsh derby victory in the Guinness PRO14.
However, they were unable to fire in scrappy, and sometimes controversial, encounter with the Ospreys powering to the win.
They led at half-time thanks to an Ifan Phillips try and were handed a penalty try in the second-half to take a decisive lead.
The Blues return to the Cardiff City Stadium next Saturday, when they host the Scarlets, who go into the clash on the back of consecutive derby wins over the festive season.
Cardiff Blues were dealt a double blow less than half an hour before kick-off as both James Botham and Keiron Assiratti failed late fitness tests.
With five specialist opensides now injured, Alun Lawrence came into the starting XV and Ben Murphy and Scott Andrews onto the bench.
The Ospreys dominated the opening exchanges after Justin Tipuric and George North combined to make good yards and they kicked Cardiff Blues pinned back before a kicking battle ensued.
The visitors laid siege once more after earning a penalty from Ben Whitehouse but they were unable to muster a scoring opportunity.
Cardiff grew into the encounter and showed some neat touch when attacking from range but unforced errors saw any opportunities lost.
As the clock approached 20 minutes the game sprung into action with Jason Tovey finding space and Aled Summerhill scorching down the left. He passed inside to Tomos Williams, who beat one man but lost his support in doing so.
Possession was recycled and Cardiff Blues looked odds on to score before a deliberate knock on five metres out saw momentum lost and eventually the ball was passed over Summerhill’s head and into touch.
Rhys Webb was penalised for the offence but surprisingly was not shown a yellow card for the cynical act and the Blues settled for three points.
The lead was lost on 33 minutes as a pair of successive penalties saw the Ospreys set up on the five-metre line. Adam Beard took the ball in the middle and Cardiff Blues were unable to repel the forward charge as Ifan Phillips burrowed over.
Myler added the extras but the Blues almost instantly had the opportunity to give the Ospreys a dose of their own medicine.
They went to the corner and set up a driving maul with the Ospreys infringing again. The Blues turned down a shot at goal and went back to the corner but the throw was not straight and the scoring chance lost.
There was controversy in the final minutes of the half as Jason Tovey was downed by an elbow to the throat and chin area. Replays showed Dan Lydiate led with his forearm and unintentionally caught the fly-half.
Whitehouse was correctly swaying towards a red card for the unfortunate Ospreys star but TMO Rhys Davies convinced the referee otherwise and the duo settled for a yellow card.
Cardiff had further opportunities in the dying moments of the half but they were held out by the fired up visitors and left empty handed with score remaining 3-7.
Wales’ Capital Region returned for the second half with fire in their bellies and a superb turnover from Shane Lewis-Hughes won a penalty. However a succession of mistake undid the hard work and Myler soon had the chance to stretch his team’s lead.
Fortunately, his effort fell short and wide and Mulvihill’s men were able to reset. They instantly went on the attack with Lee-Lo and Josh Adams combining beautifully but the move soon broke down.
Back came the Ospreys and they went to the corner once more before securing another penalty. That saw Seb Davies sin-binned and while the hosts survived unscathed Myler slotted a penalty on 55 minutes to make it 3-10.
The Ospreys all but secured the result on the hour mark when a powerful driving maul saw Whitehouse award a penalty try and sin-bin Dmitri Arhip.
Cardiff Blues desperately fought back with a rampaging break from Shane Lewis-Hughes, but that turned out to be the hosts' only opportunity in the latter stages, with Ospreys on top in the possession and territory battle.
Scott Andrews became the third man sent to the sin bin for repeated infringement, while the final moments saw Garyn Smith stretchered off after receiving a lengthy treatment.