Ospreys moved up to second position in the PRO12 standings after they beat Welsh rivals the Scarlets 19-9 at Liberty Stadium on Tuesday.
In a nervy opening half, Rhys Patchell's three penalties to Dan Biggar's two took the Llanelli-based outfit into a 9-6 advantage at the interval.
However, the hosts dominated the second period and, after a penalty try had given them the lead, their fly-half secured the win via successive three-pointers.
Both these sides have enjoyed a positive first half to the season and, as a result, the first 20 minutes was a tense affair. With defences on top, it ultimately came down to discipline and it was Wayne Pivac's men who yielded first, giving a penalty away at a scrum from which Biggar converted.
After Patchell had equalised, the Ospreys were handed an opportunity to put pressure on the opposition rearguard when Rob Evans was sin-binned for a high tackle, but the hosts could not take advantage.
It was confidence the visiting forwards took into the set-piece as they began to control the exchanges up front. Patchell duly gave them the lead from the tee before an excellent shove allowed the Scarlets' fly-half to increase their buffer to six.
Biggar did reduce the arrears on the stroke of half-time and they took that momentum into the second period, dominating possession and territory.
Eventually their pressure was rewarded following a maul which sent the away side backwards. With Steve Tandy's team about to cross the whitewash, Will Boyde came in from the side and collapsed the drive. Referee Andrew Brace therefore had no other option than to sin-bin the flanker and award a penalty try as the Ospreys moved 13-9 in front.
Even after Boyde had returned, the Scarlets' discipline remained an issue and another Biggar three-pointer helped the Swansea outfit maintain their control on the match.
With Pivac's men struggling to exit their own half, they received a third yellow card when Steff Evans was sent from the field.
Although the hosts initially failed to take advantage of the subsequent five-metre line-out, the visitors inevitably infringed in the next passage of play and Biggar sealed the win.
Try: Penalty Try
Pens: Biggar 4
Pens: Patchell 3
Yellow Cards: D Evans (23 min), Boyd (53 min), S Evans (70 min)
Ospreys: 15 Sam Davies, 14 Keelan Giles, 13 Ashley Beck, 12 Josh Matavesi, 11 Dan Evans, 10 Dan Biggar, 9 Brendon Leonard, 8 Dan Baker, 7 Justin Tipuric, 6 James King, 5 Alun Wyn Jones (c), 4 Rory Thornton, 3 Ma’afu Fia, 2 Sam Parry, 1 Nicky Smith
Replacements: 16 Scott Baldwin, 17 Paul James, 18 Rhodri Jones, 19 Lloyd Ashley, 20 Olly Cracknell, 21 Sam Underhill, 22 Tom Habberfield, 23 Kieron Fonotia
Scarlets: 15 Liam Williams, 14 Johnny McNicholl, 13 Hadleigh Parkes, 12 Scott Williams, 11 DTH van der Merwe, 10 Rhys Patchell, 9 Gareth Davies, 8 John Barclay, 7 Will Boyde, 6 Aaron Shingler, 5 Tadhg Beirne, 4 Jake Ball, 3 Samson Lee, 2 Ken Owens (c), 1 Rob Evans
Replacements: 16 Ryan Elias, 17 Wyn Jones, 18 Werner Kruger, 19 Tom Price, 20 Josh Macleod, 21 Jonathan Evans, 22 Dan Jones, 23 Steff Evans
Referee: Andrew Brace (Ireland)
Assistant Referees: Dan Jones (Wales), Wayne Davies (Wales)
TMO: Tim Hayes (WRU)