Ospreys centre James Hook crosses for a first-half try
The Ospreys proved too physical for the Scarlets as they recorded a crushing bonus-point win in the weather-delayed west Wales Magners League derby.
A James Hook try and five Dan Biggar kicks gave them a 20-3 half-time lead.
Indiscipline then cost the visitors, Jon Thomas and Biggar crossing with ex-Osprey Martin Roberts in the sin bin.
Gareth Maule got a score back, but when Sean Lamont saw yellow Richard Fussell, Tommy Bowe and Paul James crossed to secure the bonus point.
Jonny Fa'amatuainu got a consolation try for the Scarlets with Ospreys replacement Ian Evans in the sin bin, before Jamie Nutbrown completed the rout with a last-minute try from a short-range scrum.
The Ospreys leap-frog their great cross-Loughor rivals to move to second in the table and have now recorded seven successive wins in west Wales derbies.
The traditional local rivalries had been stirred further by the Scarlets' criticism of the handling of the postponement of the game from Boxing Day.
Frozen pipes at the Liberty Stadium had caused the 24-hour delay and had a knock-on effect on the crowd, the attendance a little short of the original sell-out.
In the early exchanges Dan Newton's fine break from the centre of the pitch set the visitors on the front foot, the reward coming when Rhys Priestland nailed a difficult penalty from the sidelines.
The Ospreys fired back, Thomas stealing a line-out in the Scarlets' 22, allowing Bowe to grubber kick through the defence.
Barry Davies gathered and grounded over the visitors' line, but referee James Jones awarded a borderline offside decision against the full-back, causing howls of dismay from the Swansea crowd.
Richard Fussell's try secured the Ospreys' bonus point
The Scarlets then strayed offside from a Roberts box kick, allowing 26-point man-of-the-match Biggar to level the scores with a penalty.
Biggar and Morgan Stoddart started the first scuffle of the game, the Scarlets wing penalised for throwing the ball away to give his brawling partner his second kick of the game.
Biggar stretched the lead with a wobbly, long-range penalty after the outstanding Marty Holah forced Fa'amatuainu to hold on on the floor, the physical Ospreys ruling at the breakdown.
Three Richard Hibbard line-out put-ins went astray, but when opposite number Matthew Rees overthrew one near halfway it led to the first try of the game.
Richard Fussell broke well, feeding Bowe who carried forward before finding Hook, who sprinted in at the corner.
Biggar missed the conversion, but extended the lead to 17-3 with a kick from in front of the posts when Iestyn Thomas was penalised for dropping the scrum.
The fly-half then rounded off a dominant half for his side with his fifth kick as the Scarlets were again penalised at the scrum.
To compound the visitors' problems, Roberts was sent to the sin bin at the start of the second half after he swore at referee Jones.
The Ospreys powered into the visitors' 22, the 14-man defence stretched too far as Thomas crossed in the corner for an unconverted try.
The Scarlets then saw Stoddart and Johnathan Edwards limp off injured, Ben Morgan also taken off in a tactical substitution.
The disasters for the Llanelli-based region continued, Priestland making a delightful break from his own 22, but then kicking the ball into the hands of his opposite number Biggar, who ran in unopposed from halfway for the third try.
The Ospreys contrived to lose a scrum against the head in their 22, allowing Lamont to drive powerfully for the line.
The Scotland international was held up, but the visitors regained a sliver of hope when the ball was spread wide for Maule to cross for a try that was superbly converted by Priestland.
Lamont went from hero to villain, though, the wing sin-binned for a shoulder charge in an untidy tackle on Mike Phillips.
The home side again immediately made the extra man count, spinning the ball across the line to Fussell, who stepped superbly off the left wing for the bonus-point try.
A powerful run from replacement prop James again took the Ospreys into the 22, the ball spun across the line where Bowe juggled in midfield before cantering over.
A short-range forward surge from a line-out gave James the sixth try that broke the 50-point mark, Hook putting over the conversion.
Ospreys replacement Evans was sent to the sin bin for illegal use of the boot on Fa'amatuainu, a fine run from Newton then winning the Scarlets an attacking penalty against the depleted home side.
Fa'amatuainu tapped quickly, sneaking over from close range for his side's second try.
But the Ospreys' perfect day was completed when scrum-half Nutbrown nipped over after a series of Scarlets scrum offences.
Ospreys: Barry Davies; Nikki Walker, Tommy Bowe, James Hook, Richard Fussell; Dan Biggar, Mike Phillips; Duncan Jones, Richard Hibbard, Adam Jones, Ryan Jones, Alun Wyn Jones (capt), Jerry Collins, Marty Holah, Jonathan Thomas. Replacements: Huw Bennett, Paul James, Craig Mitchell, Ian Evans, Justin Tipuric, Jamie Nutbrown, Andrew Bishop, Sonny Parker.
Scarlets: Dan Newton; Morgan Stoddart, Gareth Maule, Regan King, Sean Lamont; Rhys Priestland, Martin Roberts; Iestyn Thomas, Matthew Rees (capt), Simon Gardiner, Jonny Fa'amatuainu, Dominic Day, John Turnbull, Jonathan Edwards, Ben Morgan. Replacements: Ken Owens, Rhodri Jones, Phil John, Rob McCusker, David Lyons, Tavis Knoyle, Jonathan Davies, Lee Williams.
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