Ospreys (14) 17
- Tries: Beck, Natoga
- Cons: Biggar (2)
- Pen: Biggar
Ospreys completed a festive double over Scarlets in the Pro12 to gain ground on leaders Munster.
After a scrappy start, Ospreys centre Ashley Beck crashed over from close range, after an attack on half-way sparked by scrum-half Rhys Webb.
Priestland scored a penalty before Ospreys scored a second try as full-back Sam Davies' long pass put Fijian winger Aisea Natoga in the corner.
Scarlets dominated the second half but Ospreys held out for the win.
It means Simon Easterby's side have not beaten their West Wales rivals since 2007 and are still searching for their
first victory since November.
Despite the defeat they are up one place in seventh in the Pro12 after gaining a losing bonus point.
The Ospreys meanwhile move up to second, closing the gap to just four points on leaders Munster who
lost away at Ulster.
Steve Tandy's men went into the match hoping to complete a hat-trick of Welsh derby wins having
beaten Cardiff Blues
on 20 December and the
Scarlets on Boxing Day.
His side had the better of the first period at a wet and windy Liberty Stadium notching up a 14-3 lead at the interval.
The Scarlets had started brightly and had the chance to take an early lead but Priestland's fifth minute penalty fell just short.
Both defences dominated for the first quarter before Ospreys scrum-half Webb cut through the Scarlets defence on half-way to set up the first try.
He released full-back Davies and Beck picked up from the breakdown to power over close to the posts before Dan Biggar added the conversion.
Shortly before half-time Scarlets reduced the deficit to just four points thanks to a Priestland penalty.
A pin-point kick to touch by Biggar just seconds from the restart gave Ospreys an attacking line out just five metres from the Scarlets line.
The ball was spread wide and Davies' long pass put Natoga over, Biggar adding the conversion from the touchline.
Five minutes after the break Biggar kicked the Ospreys into a 14-point lead and it looked as if the hosts would cruise to a comfortable victory.
Priestland added three penalties to drag his side to within five points as Scarlets fought back, dominating territory and possession.
With 12 minutes to go the Ospreys were reduced to 14 men when Natoga was yellow-carded for a deliberate knock-on.
Scarlets pressed but the Ospreys defence held out to secure their fourth win in a row.
Sam Davies; Aisea Natoga, Ben John, Ashley Beck, Jeff Hassler, Dan Biggar, Rhys Webb, Duncan Jones, Richard Hibbard, Aaron Javis, Alun Wyn Jones (Capt), Ian Evans, Tyler Ardron, Sam Lewis, Joe Bearman.
Scott Baldwin for Hibbard (64); Ryan Bevington for Duncan Jones (64), Adam Jones for Jarvis (57), James King for Evans (67), Morgan Allen, Tom Issacs for John (54), Tom Habberfield for Webb (57), Richard Fussell for Ardron (74).
Gareth Owen; Kristian Phillips, Nick Reynolds, Scott Williams, Frazier Climo, Rhys Priestland, Rhodri Williams, Phil John, Emyr Phillips, Samson Lee, Jake Ball, George Earle, Josh Turnbull, John Barclay, Rob McCusker (Capt).
Kirby Myhill; Rob Evans for John (77), Jacobie Adriaanse, Johan Snyman, Aaron Shingler for Turnbull (67), Gareth Davies for Rhodri Williams (54), Aled Thomas, Jordan Williams for Owen (74).
Nigel Owens (WRU)
Ian Davies, Jon Mason (both WRU)
Ray Wilton (WRU)
Derek Bevan (WRU)