Ospreys took the bragging rights from Saturday's Welsh derby with a tense 13-6 win over Cardiff Blues.
Injuries to Sam Warburton and Dan Biggar caused concern as the match started slowly, but a Jarrod Evans penalty gave Blues a half-time lead.
The ankle injury sustained by Warburton forced him off having originally tried to play on having been strapped up after rolling his ankle.
Biggar was also injured for Ospreys in what was a first half punctuated by mistakes and a lack of quality rugby in the Swansea rain.
Evans scored a second penalty after the break giving his side a six-point lead before a try from World Rugby Player of the Year nominee Alun Wyn Jones, which eventually proved to be the edge in what was a low-key affair finishing 13-6 to the hosts.
The Blues went ahead in the sixth minute through Evans' penalty as the visitors' captain Warburton was forced off after 31 minutes, replaced by Macauley Cook.
Evans missed a penalty in the 38th minute to bring what was a quiet first half to a close with the scores at 0-3.
Sam Davies replaced Dan Biggar for the Ospreys at half-time following injury to the fly-half and missed a penalty in the 43rd minute.
The visitors finally put some more points on the board with another penalty kick from Evans before Ospreys put themselves into the lead in the 58th minute with a try from Jones, who crossed the whitewash from close range.
Sam Davies converted to give the hosts a 7-6 lead and then extended the Ospreys' advantage with a penalty in the 69th minute after a Blues tackler was penalised for not rolling away.
Davies missed a chance to put the hosts into an even stronger lead as he missed a drop goal attempt in the 74th minute.
However, he made amends as he scored a penalty with two minutes to go to secure a 13-6 victory for the Ospreys.
Pens: Davies 2
Pens: Evans 2
Ospreys: 15 Dan Evans, 14 Tom Grabham, 13 Jonathan Spratt, 12 Hanno Dirksen, 11 Eli Walker, 10 Dan Biggar, 9 Brendon Leonard, 8 Dan Baker, 7 Justin Tipuric, 6 Dan Lydiate, 5 Rory Thornton, 4 Alun Wyn Jones (c), 3 Dmitri Arhip, 2 Sam Parry, 1 Ryan Bevington.
Replacements: 16 Scott Otten, 17 Nicky Smith, 18 Aaron Jarvis, 19 Lloyd Ashley, 20 James King, 21 Tom Habberfield, 22 Sam Davies, 23 Ben John.
Cardiff Blues: 15 Dan Fish, 14 Blaine Scully, 13 Rey Lee-Lo, 12 Gavin Evans, 11 Tom James, 10 Jarrod Evans, 9 Lloyd Williams, 8 Manoa Vosawai, 7 Sam Warburton, 6 Josh Turnbull, 5 James Down, 4 Lou Reed, 3 Taufa'ao Filise, 2 Kristian Dacey, 1 Gethin Jenkins (c)
Replacements: 16 Ethan Lewis, 17 Sam Hobbs, 18 Craig Mitchell, 19 Jarrad Hoeata, 20 Macauley Cook, 21 Tavis Knoyle, 22 Gareth Davies, 23 Tom Isaacs.
Referee: Nigel Owens
Assistant Referees: Leighton Hodges, Wayne Davies
TMO: Gareth Simmonds