Two second-half penalty tries proved crucial as Ospreys denied Southern Kings a first-ever win at the Liberty Stadium.
The South Africans led at the break - thanks to tries from Michael Makase and Michael Willemse, cancelling out scrumhalf Tom Habberfield's earlier effort for the hosts.
But the Welsh side went back to basics in a scrappy second half and forced two penalty tries from a driving scrum before Jeff Hassler secured a bonus point with a late fourth.
The Kings remain winless this season while Ospreys close the gap between them and fifth-placed Connacht in Conference A.
Ospreys had not won in their previous five games but they started on the front foot here, with their forwards impressing at the breakdown in wet conditions.
The set-piece was always going to be vital and it paid off for Ospreys within 10 minutes when captain Habberfield scampered over off the back of a scrum.
But the Kings are notoriously dangerous from open play and levelled the score in some style after the break.
Some quick hands from the centres opened up space out wide and pacey wing Makase burst through to score in the corner - with Martin du Toit nailing the conversion.
It got worse for Ospreys minutes later when wing Dewi Cross limped off with an injury, replaced by Hanno Dirksen.
The Kings gradually grew in confidence and they pounced just before the break as captain Willemse powered over from close range.
The Ospreys piled on the pressure in the second half with a string of pick-and-go attempts near the try-line but replacement Nicky Smith was held up just at the crucial moment.
A series of Ospreys scrums did not come off and prop Johan Smith was sin-binned for several infringements.
But the hosts continued to ramp it off and it finally worked in the 66th minute when referee David Wilkinson awarded a penalty try after a powerful drive from the scrum.
The Kings were reduced to 13 men shortly after the kick off when Eital Bredenkamp was yellow carded at the breakdown.
And Ospreys' forwards got to work, securing a second penalty try from another scrum before Hassler crossed in the corner.
Tries: Habberfield, Hassler, Penalty tries 2
Cons: Davies, penalty tries don't require conversions
For the Southern Kings:
Tries: Makase, Willemse
Cons: Du Toit
Yellow cards: Johan Smith (Southern Kings, 64), Eital Bredenkamp (Southern Kings, 68)
Ospreys: 15 Dan Evans, 14 Jeff Hassler, 13 Kieron Fonotia, 12 Owen Watkin, 11 Dewi Cross, 10 Sam Davies, 9 Tom Habberfield, 8 Rob McCusker (captain), 7 Justin Tipuric, 6 Olly Cracknell, 5 James King, 4 Adam Beard, 3 Ma'afu Fia, 2 Sam Parry, 1 Rhodri Jones.
Replacements: 16 Scott Otten, 17 Nicky Smith, 18 Dmitri Arhip, 19 Guy Mercer, 20 Will Jones, 21 Reuben Morgan-Williams, 22 Luke Price, 23 Hanno Dirksen.
Southern Kings: 15 Masixole Banda, 14 Yaw Penxe, 13 Berton Klaasen, 12 Luzuko Vulindlu, 11 Michael Makase, 10 Martin du Toit, 9 Rowan Gouws, 8 Ruaan Lerm, 7 Martinus Burger, 6 Andisa Ntsila, 5 Bobby de Wee, 4 Stephan Greeff, 3 Pieter Scholtz, 2 Michael Willemse (captain), 1 Schalk Ferreira.
Replacements: 16 Stephan Coetzee, 17 Johan Smith, 18 Luvuyo Pupuma, 19 Jurie van Vuuren, 20 Eital Bredenkamp, 21 Godlen Masimla, 22 Barend Janse van Rensburg, 23 Harlon Klaasen.
Referee: David Wilkinson (Ireland)
Assistant referees: Stuart Gaffkin (Ireland), Richard Kerr (Ireland)
TMO: Simon McDowell (Ireland)