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Ospreys' Dan Biggar challenges Scarlets full-back Liam Williams at the Liberty Stadium

Ospreys (6) 19 Tries: Penalty Cons: Biggar Pens: Biggar 4 Scarlets (9) 9 Pens: Patchell 3

Ospreys rose to second in the Pro12 table as they ground out a victory over west Wales rivals Scarlets.

Rhys Patchell's three first-half penalties to Dan Biggar's two put the visitors ahead at the break.

A penalty try and Biggar's boot rewarded Ospreys after the break as he topped 2,000 points for the region.

Scarlets also had three players sin-binned, Rob Evans for a high tackle and Will Boyde and Steffan Evans for dragging down mauls.

There was little to commend the opening period in which defences dominated attacking play and tactical kicking was the route chosen to make ground.

Irish referee sin-bins Rob Evans (L) in the first half

The talking points were a high tackle and a rare penalty kick miss.

Scarlets prop Rob Evans' rash high challenge in the 23rd minute on Ospreys wing Dan Evans earned him 10 minutes in the sin-bin.

But even with their opponents a man short, Ospreys were unable to take advantage.

Home skipper Alun Wyn Jones was held up over the line and even before the video ref offered his verdict, the Wales lock's wry grimace indicated he had not scored.

Moments later, Jones was downed five metres out and a lack of support ensured Scarlets' eager defence earned them a penalty to thwart the threat.

Ospreys' Dan Baker takes on Scarlets

Back came Ospreys to give Biggar a simple shot at goal, but his miss was the most uncharacteristic moment of the half.

Visiting 10 Rhys Patchell had opened the scoring and added two more penalties while Biggar made amends with the last kick before the break.

Ospreys' change of approach after the break was rewarded after wing Keelan Giles' attack from deep took them into Scarlets' 22.

Pressure from the scrums and line-outs that followed ended with the hosts being awarded a penalty try.

The score also led to a try-line scuffle and Scarlets flanker Will Boyde being sin-binned for having dragged down Ospreys' driving maul.

Ospreys' Keelan Giles is brought down

Biggar converted and in Boyde's absence, Scarlets also lost wing DTH van der Merwe to injury and Biggar stretched the lead with a penalty.

Van der Merwe's replacement Evans dived at the feet of Ospreys' forward drive to earn his 10 minutes in the sin-bin.

Biggar also punished Evans' transgression by putting over his fourth and final penalty to ensure the home win.

Ospreys: Sam Davies; Keelan Giles, Ashley Beck, Josh Matavesi, Dan Evans; Dan Biggar, Brendon Leonard; Nicky Smith, Sam Parry, Ma'afu Fia, Rory Thornton, Alun Wyn Jones (capt), James King, Justin Tipuric, Dan Baker.

Replacements: Scott Baldwin, Paul James, Rhodri Jones, Lloyd Ashley, Olly Cracknell, Sam Underhill, Tom Habberfield, Kieron Fonotia.

Scarlets: Liam Williams; Johnny McNicholl, Hadleigh Parkes, Scott Williams, DTH van der Merwe; Rhys Patchell, Gareth Davies; Rob Evans, Ken Owens (capt), Samson Lee, Jake Ball, Tadhg Beirne, Aaron Shingler, Will Boyde, John Barclay.

Replacements: Ryan Elias, Wyn Jones, Werner Kruger, Tom Price, Josh Macleod, Jonathan Evans, Dan Jones, Steff Evans.

Referee: Andrew Brace (IRFU)

Assistant referees: Dan Jones, Wayne Davies (both WRU)

Citing commissioner: Aurwel Morgan (WRU)

TMO: Tim Hayes (WRU)