Cardiff claimed what could be a crucial 1-0 South Wales derby victory over bitter rivals Swansea at the Liberty Stadium thanks to Aden Flint's early goal.
Flint has now scored more goals in English League football than any other defender since August 2014 and his 38th effort in that time gave Cardiff their first derby win since 2013, as he headed home in the eighth minute.
Success for the Bluebirds means neither Swansea nor Cardiff have ever done the derby double in the same season. Swansea had been 2-0 winners at Cardiff City Stadium earlier in the campaign.
Swansea handed a first start to 20-year-old Morgan Whittaker in attack with Jamal Lowe – their two-goal hero in the reverse fixture – on the bench.
Cardiff, meanwhile, were without in-form right-back Perry Ng.
Swansea's Conor Hourihane was fouled by Will Vaulks on the edge of the box early on.
Hourihane stepped up and curled a free-kick towards goal which Dillon Phillips tipped wide for a corner. Cardiff responded by taking the lead from a trademark set-piece.
Vaulks launched in a long throw and it fell to Marlon Pack, whose poked effort on goal was brilliantly saved by Swansea goalkeeper Freddie Woodman but Flint reacted quickest to power home a header.
Swansea's eagerness to play out from the back was being tested by Cardiff's impressive pressing and Leandro Bacuna forced Woodman into action again from an away counter-attack.
Swansea's strife was not improved by them losing key man Hourihane who had initially tried to run off a thigh muscle injury. Korey Smith was the man to come on.
Cardiff captain Sean Morrison also headed a monster Vaulks free-kick wide, while Swansea's Jay Fulton and Matt Grimes put speculative efforts over the bar.
Just before the break, a Woodman error played in Cardiff striker Kieffer Moore who ran in on goal but could not convert. Ryan Bennett got back to clear the danger.
The pace of Swansea's game improved at the start of the second period and Whittaker had a shot saved. Andre Ayew was then fouled on the edge of the box by Vaulks to earn a home free-kick.
Ayew curled the resulting effort wide, with Phillips unbothered.
Whittaker also blazed over when he should have at least hit the target, while at the other end Woodman denied Harry Wilson on another counter. Wilson had been quiet to that point.
Ayew came within inches of levelling the scores when his header from a Connor Roberts corner beat Phillips but not the post.
Swansea introduced Lowe and Ryan Manning and switched to a back four in search of an equaliser, but although they dominated the ball, they could not break through.
