Second-half tries from Dan Parks and Tom James sealed a 21-14 victory over their fellow Heineken Cup quarter-finalists in front of a 8,600-strong crowd at the Arms Park.
A second success in as many weeks at their old home in the centre of the capital saw the Blues jump into fourth spot in the standings having played a game less than leaders Leinster and second-placed Ospreys.
An early Robbie Diack score signaled a poor start for the Blues against a visiting team who arrived in Cardiff on the back of three straight league wins but Gareth Baber and Justin Burnell will have been pleased with the commitment and composure their men showed to keep Ulster tryless for the remainder of the game.
A brace of penalties from scrum-half Ruan Pienaar compared to one from Blues fly-half Dan Parks saw the hosts trail 11-3 with just seconds of the first half remaining before Parks struck a superb touchline penalty to cut the gap to five points.
And while the opening 40 minutes had been almost all Ulster, the second half was a completely different story.
With a strong wind behind them, the Blues made a flying start to the second period and levelled the scores within two minutes of the restart.
Following strong build up play, Parks fired a long pass to Ben Blair who was brought down agonisingly short by Nevin Spence and Ian Whitten but Parks was on hand to dive over from close-range.
Ulster fought back with some swift counter-attacks and had the Blues on the ropes thanks to a charge down from Paddy Wallace but they were unable to take advantage of the opportunity.
And the Blues punished the Belfast-based province when Tom James ran clear a minute before the hour mark. Gavin Henson made the most of his release from the Wales squad by producing a moment of magic to release Gavin Evans, with the latter’s lovely line and pure pace tearing the Ulster midfield apart. Evans then coolly drew former Ospreys full back Stefan Terblanche to set up the in-form James for his fourth league try of the season.
Parks added the extras to hand the Blues an 18-11 lead but the recently retired Scotland international was unable to stretch it further with a penalty moments later after Ian Humphreys was sent to the sin-bin for a deliberate knock on.
Parks and Pienaar exchanged penalties to bring the scores to 21-14 with less than 10 minutes to go and that was how it stayed. Ulster never came close to scoring the converted try that would have brought the sides level, while the Blues had a third score – and a second for James – ruled out for a knock on.
