Swansea claimed the south Wales derby bragging rights against Cardiff as Ben Wilmot became the unlikely hero with the only goal in a 1-0 win.
England Under-21 defender Wilmot's first senior goal after 24 minutes settled a full-blooded Sky Bet Championship clash at the Liberty Stadium.
The 19-year-old centre-half, on loan from Watford, made his first league start for Swansea after Joe Rodon had failed a fitness test and his header took Steve Cooper's side back into the play-off places.
Swansea were the superior side throughout and should have won by more, with Cardiff producing a flat performance out of character with the passion of their manager Neil Warnock.
This was the first south Wales derby since February 2014 when Garry Monk marked his first game as Swansea manager with a 3-0 win over Ole Gunnar Solskjaer's Cardiff.
Nathan Dyer and Wayne Routledge were among the scorers that day, and the pair both started as Swansea boss Cooper made six changes in an attempt to arrest a run of poor form.
Swansea had picked up only one point from four home games, while Cardiff were also short on wins with two from their previous 10 outings.
Sean Morrison saw his early near-post effort gathered, but the captain gave Cardiff concern when he fell awkwardly and needed lengthy treatment on a wrist injury.
Swansea quickly settled into their passing rhythm with Matt Grimes and George Byers shining in midfield and Andre Ayew relishing his lone-striker role.
Ayew raced onto a 10th-minute through ball from Byers and Cardiff were grateful to Lee Peltier's goal-line intervention.
Bersant Celina almost punished goalkeeper Neil Etheridge's poor clearance from inside his own half and Grimes fired over from 20 yards as Swansea continued to press.
The pressure was rewarded after 24 minutes when Swansea worked a short-corner routine and Routledge crossed for the unmarked Wilmot to power his header home.
Morrison deflected Ayew's shot into the side-netting, with the Ghana striker heading wide from the resulting corner as Cardiff again neglected their defensive duties.
The pattern remained the same after the restart with Swansea bossing midfield and breaking quickly, and Grimes' angled drive forced Etheridge into swift action.
Celina also prodded goalwards from a Jake Bidwell cross and Etheridge again collected comfortably at his near post.
Cardiff finally stirred from their slumber, with Swansea goalkeeper Freddie Woodman saving twice in as many minutes.
Woodman shovelled away Morrison's header and then held Gavin Whyte's volley on his line after Joe Ralls delivered an excellent cross to the far post.
Dyer and Celina had chances to extend the lead, but Swansea held on to celebrate the sweetest of victories.