Two tries from Theo Cabango were not enough as Cardiff were denied at the death in devastating fashion in Belfast.
The Blue and Blacks led by a single point as full-time approached and looked to have sealed a first win at the Kingspan Stadium since 2010 when Cabango was put away for a hat-trick.
But following a TMO intervention the try was ruled out and Rhys Carré was sin-binned for what was adjudged a deliberate knock on in the build-up. At the worst it was unfortunate for Carré and despite several replays the incident remained unclear but the decision was made and John Cooney stepped up to slot the controversial penalty.
With just a minute remaining, the Blue and Blacks had little chance to retrieve a victory and were instead left with a losing bonus-point for the ninth time this season.
Cardiff were boosted by the return to fitness of Taulupe Faletau for the trip to a sun-kissed Kingspan Stadium in Belfast. The number-eight had recovered from a broken arm and calf injuries to make his long-awaited first appearance of the season.
But to compound the club’s woes, Faletau was helped off while clutching his arm in the first-half.
In total Matt Sherratt made four changes to the starting team with Teddy Williams, Young and Faletau replacing Seb Davies, Ellis Jenkins and Mackenzie Martin in the forwards, and Theo Cabango coming in for Owen Lane.
Cardiff were dealt a blow when Cam Winnett left the field of play after just three minutes. The Wales full-back landed heavily after being taken out in the air and stayed down following his next involvement.
Ulster had an early opportunity to turn the screw with a kick to the corner but Nathan Doak put the ball dead.
Where Doak failed, De Beer stepped up with a monstrous penalty to the corner but after winning a clean lineout, Cardiff lost the ball at the breakdown.
However, on the Blue and Blacks next venture to the corner they struck with a slick set play. The ball was won and Thomas Young played the ball from the back to Ellis Bevan, who then popped a ball back inside to Cabango.
The wing beat two men to claim a try on his return to the starting line-up following injury. De Beer added the extras.
As the half-hour mark approached a loose kick saw Ulster enjoy long periods of possession and they stretched Cardiff from left to right before settling for a penalty.
Cardiff were dealt a further blow when Faletau was helped off clutching his arm on the 30th minute.
Ulster continued to pile on the pressure and twice kicked penalties to the corner, although the second was fortunate after the TMO called a technical offence at the lineout.
Cardiff again matched Ulster’s physicality and Ben Thomas and De Beer did remarkably well to hold Dave Ewers up over the line and the fly-half then cleared.
Moments later however, Ulster were given a third penalty in quick succession and opted for the sticks with Doak converting to make it 6-7 at half-time.
Cardiff once again started the half brightly and claimed a second try after just three minutes of the restart thanks to that man Cabango.
The Blue and Blacks were intent on attacking and keeping the ball in play and were in danger of losing shape when Thomas fired a long, flat pass to release Cabango on the wing.
He scorched outside Jude Postlethwaite and then stepped inside the last man to cross for a stunning second.
De Beer added the extras to make it 6-14 and moments later Cabango had a sniff of a hat-trick from a counter-attack but Mike Lowry recovered for a try-saving tackle.
Cardiff continued to enjoy opportunities in a highly entertaining encounter but perhaps lacked a accuracy at key moments.
It proved costly when Ulster hit back through Dave McCann despite what appeared to be a knock-on at the line out, which was not looked at.
John Cooney, on as a replacement, slotted the conversion to cut Cardiff’s advantage to a single point.
With decisions continuing to go against the Blue and Blacks, Cooney nudged the home side into the lead for the first time on 65 minutes.
Cardiff almost responded with a candidate for try of the season as offloads out the back from Markenzie Martin and Jacob Beetham, followed by quick hands from Grady and Gonzalo Bertranou released Thomas Young down the right.
He raced cleared crossed the whitewash but just as he attempted to ground the ball, a stray leg from the tackler dislodged the ball in a devastating blow.
Next it was Bertranou, who almost broke clear but Ulster covered well and he ran out of support but with ten minutes later De Beer nudged Cardiff back in front.
Ulster then came storming back and threw everything at the Blue and Blacks but Ellis Jenkins, with Ulster players flying at him from all angles, claimed a trademark turnover to relieve the pressure.
The home side threw everything at Matt Sherratt’s men in the closing stages but the visitors were unrelenting in defence.
With less than two minutes to spare the ball came loose and razor-sharp minds and hands saw the Blue and Blacks race the length of the pitch with Cabango crossing for his would-be hatrick.
However, the TMO intervened and play was brought back. Following several replays Carré was sin-binned and Ulster handed a penalty which Cooney converted for a slender win.