Luck was not on Ulster's side in the Welsh capital. They lost both Clinton Schifcofske, their first choice place-kicker, and Ireland back-up fly-half Paddy Wallace to injury in the opening quarter-hour.

Charged with the place-kicking duties, young number 10 Niall O'Connor missed two kickable penalties either side of half-time when the visitors could have bolstered their lead to 14-6.

But Ulster will take collective blame for failing to see out the result. Cardiff, thanks to an improved second half display, bounced back to snaffle the four points with full-back Ben Blair again playing a central role.

Wearing their alternate pink jerseys to support Cancer Research Wales, Cardiff were playing for points and pride after they were criticised for their Tuesday night collapse to the table-topping Ospreys.

Head coach David Young made nine changes to the side that lost 32-10 at the Ospreys, with Gareth Thomas, Nicky Robinson, Gethin Jenkins, Paul Tito, Maama Molitika and Martyn Williams amongst the players recalled.

Ulster tweaked their starting line-up before kick-off - Matt Williams brought O'Connor and prop Tom Court in for the benched Rob Dewey and Justin Fitzpatrick.

Ireland 'A' internationals Ryan Caldwell and David Pollock were also included, having missed last week's 16-9 reversal to the Scarlets at Ravenhill.

And both Caldwell and Pollock were prominent in the loose during the opening stages of the game, as Ulster looked to establish a foothold.

With sloppy passing in the backs and a lack of bite up front costing Cardiff, Ulster dictated play for much of the first half despite shipping those injuries.

Their pack was immense and it was no surprise when a forward rumble led to their first try, 11 minutes into the fray.

Darren Cave made a half-break and some forward grunt, off the back of a lineout, was finished off by World Cup winner BJ Botha who powered over from close range for his first Ulster try.

Schifcofske was off target with the conversion attempt but the Blues, whose back rowers were being swallowed up by Ulster's tigerish tackling, knew they were in a game.

The hosts' early expansiveness, when Leigh Halfpenny threatened with a kick-and-chase, went out of favour quickly as they opted to keep things tight in the second quarter.

Maybe three games in the space of six days, against the competition's three most recent champions, took its toll?

Still, their reward for some diligent forward play was two penalty successes for New Zealander Blair after 17 and 32 minutes.

In between, O'Connor slammed over a penalty at the other end to help Ulster on their way to an 8-6 half-time lead.

Of course, they should have been further in front at that stage and the efforts of captain Rory Best, in particular, and their territorial edge merited more.

Nonetheless, had Cardiff's Nicky Robinson been on the money with either of his two drop goal attempts before the break, Williams' men would have been in arrears.

Armed with that two-point buffer, Ulster tried manfully to keep on track in the second half as they eyed their first win on Welsh soil since September 2006.

However, Williams and his coaching staff were left frustrated by what they saw after the break.

The Australian, who guided Leinster to the inaugural league title in 2001, bemoaned his side's lack of structure in the second period, conceding that 'the effort was there alright but we were running round like headless chickens.'

They did get over for a second try when scrum half Isaac Boss slipped past Jamie Robinson and touched down behind the posts, for O'Connor to convert them into a 15-13 advantage.

But Cardiff, showing better control and keeping themselves in the Ulster half and 22, kept chipping away.

Their comeback was all the more noteworthy given that Martyn Williams' night was ended by an ankle injury.

Man-of-the-match Maama Molitika, who is having a great start to the season, was in excellent ball-carrying form as Cardiff took the game to Ulster.

The visitors' loss of discipline cost them as after a Blair penalty had hit the post, they quickly got back in range for Leigh Halfpenny to notch a try.

Replacement fly-half Ceri Sweeney offloaded for the teenager to power over under the posts and Blair's conversion had the Blues 13-8 ahead.

A powerful charge forward from replacement flanker Kieron Dawson, after an interception, showed Ulster had no intention of giving up without a fight.

Andrew Trimble also threatened out wide and he was stopped just short of the line, coming up to the hour mark.

The try-scoring chance was almost lost but after a bout of sustained pressure, Boss crossed the whitewash in the 69th minute.

Two points adrift again, Cardiff did not panic and just two minutes later Blair raised the flags of the assistant referees once more to strike the telling blow.

After watching his side claim their fourth win on the trot over Ulster and open their win account for the season, David Young was a relieved man.

"We're a team that didn't play with a lot of confidence, we were poor with the ball on a lot of occasions," he said.

"But I thought we showed a lot guts and determination because the boys could've thrown the towel in at one stage. It was a good win and one we needed after a tough schedule of games."