Alun Wyn Davies’ side ran in five tries as they blew Swansea away in front of a healthy student crowd.
Pat Lewis crossed before the break with a superb, individual effort, before Harry Griffiths, Louie Silver, Chris Williams and Aron Hughes all went over in the second half.
It was one win apiece between the two teams in this season’s BUCS; Swansea 10-8 winners in November with Cardiff thumping their biggest rivals 43-8 in November.
Nerves were clear in the early exchanges as both sides struggled to hang on to the ball.
Phil Jones had the opportunity to break the deadlock five minutes in, but his penalty fell way short of the target.
Julian Mogg blew a golden chance for Cardiff when with an overlap on and Rhodri Wall outside him, the full-back opted to take it alone rather than pass.
But Swansea scored the first points when Rory Garrett – who secured the winning points in last season’s win – remained ice-cool with a drop-goal attempt from 35 yards.
And the Green & Whites thought they had the game’s first try, but Will Jones spilled the ball on the try line after breaking through a Chris Williams tackle.
But Cardiff marched back and made Jones pay for his calamity. Mogg wriggled his way out of trouble and found Lewis via hooker Jack Haines.
The wing kicked over the top, gathered on the bounce, and dived over behind the posts with James Davies adding the extras.
Jones saw a penalty attempt on the cusp of half time cannon off the uprights.
After the break, Swansea began brightly.
Jones looked clean through but was halted by a charging Mogg in the corner and minutes later Garrett skewed a penalty well wide.
Again there was no mistake from the men in red as they raced further ahead. Centre Griffiths – who scored a try in last year’s loss – battled his way over in the corner with Davies impressively kicking the conversion.
And minutes later replacement scrum-half Silver added to Cardiff’s lead, taking a quick tap and go to cross at the posts.
No 8 Williams crossed for try number four after he collected Davies’ cross-field kick before sliding over.
Outside-half Davies remained perfect from the tee with the two points.
Former Cardiff Blues and Wales Sevens ace Richard Smith battled his way over for Swansea’s only try with Jones able to split the uprights with the conversion.
But flanker Hughes put the cherry on top for Cardiff with their fifth try before Swansea battled over for a last-ditch consolation.
