Ulster's season took a further nose dive as they lost a third straight Guinness PRO14 match.
The loss at the Arms Park on Saturday afternoon leaves them 13 points behind Edinburgh in Conference B of the PRO14 and their hopes of a Championship play-off spot and automatic qualification to the European Champions Cup as good as gone.
Ulster are also feeling the pressure as fifth place Benetton Rugby picked up a bonus point win in a 36-35 away win at Southern Kings earlier in the afternoon.
The Blues - who are chasing an automatic European Champions Cup place in Conference A - signalled their intentions after just two minutes when outhalf Jarrod Evans crossed for a try and added the conversion.
Ulster responded well and an infringement from former star Nick Williams offered scrumhalf John Cooney a penalty opportunity which he slotted over after five minutes.
Blaine Sully went over for a try for the Blues on 12 minutes, converted by Evans and although the Welsh side had a numerical advantage after Ulster prop Wiehahn Herbst was yellow carded for a dangerous tackle, it was the visitors who got the next points - another penalty from Cooney.
But Evans sent Cardiff in at the break leading 17-6 with a penalty in added time.
Ulster had started the second half positively and two Cooney penalties on 41 and 51 minutes brought them back into the game at 17-12, offering some hope.
But the usual poor handling, ill discipline and mistakes which have haunted them all season continued and when replacement hooker Kristian Dacey crossed on 57 minutes the game was getting away from the Irish Province.
Evans kicked two further penalties on 63 and 70 minutes to make it 28-12 and although Ulster rallied towards the end replacement Matt Dalton failed to get the ball down when he was over the line.
A minute from the end replacement scrumhalf Dave Shanahan crossed for a try, which outhalf Johnny McPhillips failed to convert.
The Blues got over for a try scoring bonus point on the third minute of overtime, replacement prop Dillon Lewis getting the try and Evans converted to complete the scoring at 35-17