The Ospreys were superior in virtually every department with the Scarlets second best from the kick-off. Halfbacks Kahn Fotuali'I and Dan Biggar pulled the strings expertly for the victors with the Samoan a constant threat from the base of the scrum. He thoroughly deserved to be crowned man of the match while Bigger did his chances of gaining the coveted Welsh No 10 shirt no harm with a controlled performance from outside half. His kicking out of hand was first class while his trusty right boot claimed another 14 points.
The Scarlets took 77 minutes to seriously threaten the Ospreys try-line but a lack of composure ensured the visitors returned empty handed.
The match was only two minutes old when the Ospreys asserted their authority at scrum time. The Scarlets pack crumpled and Biggar stepped up to get the show on the road with an easy penalty.
The Ospreys dominated the early play and showed plenty of enterprise, with Fotuali'I showing his experience when he snapped over a drop goal from a close range ruck when nothing else appeared on.
The home side saw plenty of ball with winger Eli Walker giving George North and Jonathan Davies plenty to think about with his mazy running.
Ashley Beck, Richard Fussell and Biggar all kept the Scarlets pegged back with a simple but effective kicking game plan.
Trapped near their own line, the Scarlets scrum collapsed again and referee Owens had no hesitation in awarding the penalty try. Biggar's simple conversion gave the Ospreys a 13-0 lead after 25mins.
Aled Thomas reduced the arrears with a penalty after Fotuali'I was penalised for not releasing the man in a tackle but that was to be as good as it got for the Scarlets.
Earle was sent to the cooler after knocking Fotuali'I to the ground after the Ospreys skipper took a quick tap. The Ospreys then camped inside the Scarlets 22 until the Scarlets scrum was destroyed under their own posts and Biggar stepped up to knock over another three points to give his side a 16-3 lead after 34mins.
Biggar rubbed the Scarlets noses in it further when he put the Ospreys 19-3 up at the break with the last kick of the first half after Aled Davies had made a mess of his clearance kick to put his entire pack off-side.
The Ospreys confirmed their dominance seven minutes after the break when James King slid over in the corner after prop Ryan Bevington flung out a pass Neil Jenkins would have been proud of in his pomp.
Biggar missed the touchline conversion but he soon arrowed over another penalty to keep the scoreboard ticking over.
The Scarlets made a raft of changes in the second spell to stem the flow but the Ospreys remained in control as basic handling mistakes hindered the visitors hopes of staging any form of comeback.
Replacement scrum-half Knoyle was yellow carded for an early tackle on Walker and the Ospreys struck like a viper. Without their scrum half, the Scarlets lost their own scrum. Fotuali'I picked up the crumbs and exploded down the blindside. He rode Aled Thomas's tackle to score in the corner.
Thomas's day then got worse when he was yellow carded but the procession continued as McCusker and Owen both saw red as the Ospreys waltzed to a comfortable victory to rise to fifth in the points table, just seven points behind the Scarlets who are in second place with 38 points, although they have played an extra game.