Ospreys reapplied the pressure on Leinster at the PRO12 summit after defeating Cardiff Blues 17-12 in their Welsh derby showdown on Sunday.
Indiscipline from the Blues during the opening exchanges gifted Ospreys an early lead. Matthew Morgan was on target twice with the boot in the first four minutes to give the home side a 6-0 lead.
The Blues rallied, however, and were back on level terms before the end of the first period, courtesy of two penalties from Leigh Halfpenny.
Neither side was able to cross the whitewash before the interval or further trouble the scorers, meaning there was nothing between the two Welsh rivals when the whistle blew for half time.
Ospreys crossed the whitewash and delivered the game's first try ten minutes into the second half, when the ball was worked right straight from the scrum and Tommy Bowe crashed over. The kick was missed but the hosts held an 11-6 lead.
The Blues reduced the deficit to just two points when Halfpenny struck for the third time after Ospreys had infringed at the ruck.
Then, after the home side missed a penalty, Cardiff kicked a drop-goal. The ball was flung from the ruck to the poised Dan Parks, who made no mistake from 20 metres out to give his side the lead.
But the slender advantage was cancelled out on 72 minutes when substitute Dan Biggar slotted over a penalty after Cardiff had infringed at the ruck.
Then, as the Blues desperately searched for a way back in to the game, Biggar cemented the win with a second penalty in the dying seconds.
Pen: Morgan 2, Biggar 2
For Cardiff Blues:
Pen: Halfpenny 3
Ospreys: 15 Barry Davies, 14 Tommy Bowe, 13 Andrew Bishop, 12 Ashley Beck, 11 Shane Williams/Hanno Dirksen, 10 Matthew Morgan, 9 Kahn Fotuali'i, 8 George Stowers, 7 Justin Tipuric (Capt), 6 James King, 5 Jonathan Thomas, 4 Ryan Jones, 3 Adam Jones, 2 Richard Hibbard, 1 Ryan Bevington.
Replacements: 16 Huw Bennett, 17 Duncan Jones, 18 Aaron Jarvis, 19 Tom Smith, 20 Joe Bearman, 21 Rhys Webb, 22 Dan Biggar, 23 Tom Isaacs.
Cardiff Blues: 15 Gavin Henson, 14 Leigh Halfpenny, 13 Casey Laulala, 12 Gavin Evans, 11 Alex Cuthbert, 10 Ceri Sweeney, 9 Lloyd Williams, 8 Xavier Rush, 7 Josh Navidi, 6 Maama Molitika, 5 Paul Tito (c), 4 Bradley Davies, 3 Scott Andrews, 2 Ryan Tyrell, 1 John Yapp.
Replacements: 16 Marc Breeze, 17 Sam Hobbs, 18 Ryan Harford ,19 Michael Paterson, 20 Sam Warburton, 21 Richie Rees, 22 Dan Parks, 23 Harry Robinson.
Referee: Nigel Owens