Tommy Bowe scored two tries, one a dramatic late interception, to lift the Ospreys into the Magners league play-off places with a close 27-19 victory over regional rivals Scarlets at the Liberty Stadium on Friday.
With two minutes left on the clock and the Ospreys holding a slender 20-19 lead Irish star Bowe ran in 70 metres after picking off a Stephen Jones pass.
The defeat, their 11th of the season, leaves the Scarlets who were denied a losing bonus point, in real danger of missing out on Heineken Cup qualification.
The Ospreys named an all international starting line-up as they had for the defeat at the Dragons last week, with Lions Alun Wyn Jones, back from an elbow injury, and Shane Williams named on the replacements bench.
The Scarlets welcomed back their two Lions - Stephen Jones and Matthew Rees - for their first regional starts since the Six Nations.
Jones played amid media speculation that is being linked with a move to Leicester Tigers.
It was a typically cagey start from both sides in such a crucial local derby.
Dan Biggar's ninth minute drop goal, after a good passing move involving Ryan Jones, Nikki Walker and Andrew Bishop, was cancelled out by a Stephen Jones penalty two minutes later.
Biggar put the home side into the lead with a 17th minute penalty but again it was a shortlived advantage as the Scarlets responded with a finely worked try.
Jonathan Davies crossed after an attack involving Travis Knoyle, Rob McCusker and Rhys Priestland.
In such a nip and tuck contest, played out for much of the first half in teeming rain, the Ospreys went back into the lead albeit briefly when Bowe, Six Nations player of the tournament, crossed in the right corner after good work from Biggar, Bishop and Lee Byrne.
But again the Ospreys only led for two minutes as a Jones penalty gave the Scarlets a 13-11 advantage on 35 minutes.
With the last kick of the half, however, a Biggar penalty goal put the Ospreys into a 14-13 interval lead.
But Biggar's radar went adrift in the second half. He missed crucial penalty shots on 46 and 61 minutes.
And significantly Stephen Jones was on target with a 58th minute penalty in front of the posts which put the Scarlets back in the lead - 16-14 - for the third time.
The Ospreys thought they had a score through Byrne but referee Christophe Berdos ruled it out for a Bowe push on Andy Fenby.
But with eight minutes remaining Biggar rediscovered his range to kick the Ospreys back into a one point lead with a dropped goal.
Jones and Biggar exchanged penalties in the space of three minutes, but as the Scarlets pressed for the win Jones sent out a pass to the left touchline only to be plucked out of the air by Bowe, who ran in unopposed to the delight of most of the 13,913 in the stadium.
For the Ospreys:
Tries: Bowe 2
Pens: Biggar 3
Drop goals: Biggar 2
For the Scarlets:
Pens: Jones 4
Ospreys: 15 Lee Byrne, 14 Tommy Bowe, 13 Andrew Bishop, 12 James Hook, 11 Nikki Walker, 10 Dan Biggar, 9 Mike Phillips, 8 Ryan Jones (capt), 7 Marty Holah, 6 Jerry Collins, 5 Jonathan Thomas, 4 Ian Gough, 3 Adam Jones, 2 Richard Hibbard, 1 Paul James.
Replacements: 16 Huw Bennett, 17 Craig Mitchell, 18 Alun Wyn Jones, 19 Filo Tiatia, 20 Jamie Nutbrown, 21 Sonny Parker, 22 Shane Williams.
Scarlets: 15 Rhys Priestland, 14 Sean Lamont, 13 Regan King, 12 Jonathan Davies 11 Andy Fenby, 10 Stephen Jones, 9 Tavis Knoyle, 8 David Lyons (c), 7 Richie Pugh 6 Rob McCusker, 5 Dominic Day, 4 Lou Reed, 3 Deacon Manu, 2 Matthew Rees, 1 Iestyn Thomas.
Replacements: 16 Phil John, 17 Ken Owens, 18 Rhys Thomas 19 Damian Welch, 20 Josh Turnbull, 21 Martin Roberts, 22 Daniel Evans.
Referee: Christophe Berdos