Scarlets (9) 18
Pens: S Jones (6)
Ospreys (6) 21
Tries: Fussell, AW Jones Con: Biggar Pens: Biggar (2) DG: Biggar
Highlights: Scarlets 18-21 Ospreys
The Ospreys' superior strike power won them an intense west Wales derby at Llanelli's Parc y Scarlets.
Stephen Jones' superb tactical control and kicking gave the fired-up home side the advantage and they were unfortunate to be denied a Dan Evans try.
There was more anger as Richard Fussell scored a try after a forward pass, Alun Wyn Jones then notching the second try.
Dan Biggar got the winning drop goal, Jones, who kicked all 18 Scarlets points, short with his final penalty.
The Ospreys, who ended their rivals' three-match winning run, have now won the last five cross-Loughor derbies, maintaining their 100% record at Parc y Scarlets.
For long periods it seemed that the home side would end that run as they controlled territory and possession.
Stephen Jones' tactical control gives the Scarlets the first-half advantage
Jones missed a first-minute penalty, before opposite number Biggar put his side under pressure with an over-ambitious chip over the defence from inside his own 22.
The Ospreys were penalised for using their hands at a ruck and this time Jones made no mistake with the penalty to give his team the early advantage.
Biggar cancelled that out with a testing 42m kick after the Scarlets went offside chasing a Tavis Knoyle box kick, before referee Nigel Owens raised the ire of the near-capacity crowd.
Alun Wyn Jones knocked on as the Ospreys tried to run from their own half and the ball fell to Scarlets full-back Evans who had a clear run to the line.
But Owens had blown his whistle straight after the Jones error and apologised to the men in red for not allowing the advantage.
Ospreys full-back Lee Byrne denied Sean Lamont with a great tackle after the Scarlets winger latched onto a delightful Stephen Jones chip over the defence.
Regan King - celebrating his 30th birthday - glided past Andrew Bishop in the centre then Johnathan Edwards charged down a Byrne clearance kick as the home side continued to build the pressure.
The reward came with a 21st-minute Jones penalty, but Biggar again replied to level up the scoreboard.
The Scarlets saw in-form rookie winger George North hobble off to be replaced by Scott Williams.
But the home side's dominance of the first half got its reward when a driving maul won Jones another penalty chance that he slotted home to make it 9-6 at the break.
The Ospreys seemed to have learnt little during half-time, immediately running ball from their own 22, losing it, and gifting Jones a penalty that the fly-half slotted with ease.
The first half was pretty dire with our kicking game and what we did with possession, but we were a bit wiser after the break
Ospreys captain Alun Wyn Jones
From out of nowhere the Ospreys struck back, though, moving the ball across the three-quarter line from a ruck wide on the left just inside the Scarlets' half.
A delightful sleight of hand from Bishop created the space for Byrne to send Fussell over in the right-hand corner, much to the fury of the 13,700 Llanelli crowd who screamed at the full-back's clearly forward pass.
Biggar's conversion put the Ospreys ahead for the first time, but Jones immediately reclaimed the lead with his fifth penalty.
The frenetic action continued, Marty Holah just denied a try by Williams after the Ospreys flanker charged down Evans' kick.
Another brief burst of the Ospreys' talent saw them regain the lead, Shane Williams and Tommy Bowe combining slickly in the Scarlets' 22 to send Alun Wyn Jones over in the corner, Biggar hitting the post with the conversion.
The Liberty Stadium side brought James Hook and Ryan Jones off the bench to emphasise the quality at their disposal, but it was the Scarlets who struck back with Jones' sixth penalty levelling the scores.
With seven minutes to go a series of Ospreys drives at the Scarlets line culminated in the crucial Biggar drop goal.
Fussell crosses for a controversial Ospreys try after a forward pass
Another moment of magic from King helped win a long-range penalty shot to give the home side a last chance, but Jones' effort slid off target and short from wide on the right.
The Scarlets at least have a platform to build on ahead of next week's tough Heineken Cup opener at home to Perpignan, while the Ospreys will be boosted for their formidable trip to Toulon.
"The intensity of the derby was the equivalent of a Heineken Cup game so that's good build-up for next weekend," said Ospreys skipper Alun Wyn Jones.
"The first half was pretty dire with our kicking game and what we did with possession, but we were a bit wiser after the break."
His team-mate and man-of-the-match Jerry Collins added: "The first 60 minutes we didn't see much of the ball - it was pretty much all tackling.
"A couple of classy moves made the difference. We're just glad to get the win."
Scarlets: Evans, North, King, Maule, Lamont, S. Jones, Knoyle, I. Thomas, Rees, Manu, Reed, Day, Turnbull, J. Edwards, Lyons.
Replacements: S. Williams for North (35), R. Thomas for Manu (59), Fa'amatuainu for Day (72), McCusker for J. Edwards (59). Not Used: Phillips, John, Roberts, Priestland.
Ospreys: Byrne, Fussell, Bowe, Bishop, Williams, Biggar, M. Phillips, James, Hibbard, A. Jones, Gough, A. Jones, Collins, Holah, Thomas.
Replacements: Hook for Fussell (63), Bevington for James (58), Tipuric for Collins (73). Not Used: Bennett, Mitchell, R. Jones, Nutbrown, N. Walker.
Referee: Nigel Owens (WRU).