The Bluebirds took a surprise first half lead from the penalty spot after Diogo Dalot brought down Nathaniel Mendez-Laing in the box, who dusted himself down to bury his spot-kick and give the Bluebirds the advantage.
Mendez-Laing then scored again after the break when he tapped in from a Josh Murphy assist to compound United’s misery.
Neil Warnock’s side gave Cardiff supporters one last thing to cheer for after a difficult season in the top flight, watch GOALs and Highlights – LINK .