Celtic League/ Cardiff Blues 19; Ulster 15: Ulster coach Alan Solomons was left to rue a poor start on Saturday night as his side threw away a chance to take a lead in the race for the Celtic League title.
The visitors to a wet Arms Park were cursing lapses of concentration as a fired-up Cardiff Blues side took a 19-3 lead early in the second half, and despite a two-try finish, Ulster had to settle for a losing bonus point.
"All credit to the Blues - they probably deserved the win because they dominated the game for a long periods," a disappointed Solomons said. "We simply didn't perform from the first whistle. We nearly got the win at the end but the Blues' defence was very good indeed."
Cardiff's infamous ill-discipline nearly cost them the match. After taking a 16-point lead into the last half-hour, two yellow cards allowed Ulster to score through Simon Best and replacement Warren Brosnihan, but Ulster just failed to score the crucial third try that could have relegated Cardiff to the second tier of European rugby next season.
The last-placed Welsh region in the Celtic League this season lose their Heineken Cup spot, and a loss would have made Dai Young's players favourites for the drop. As it is, they trail the Ospreys by only three points.
Ulster's losing bonus point for finishing within seven points keeps them ahead of Llanelli Scarlets on points difference.
Ulster were slow out of the blocks in the rain, and a missed clearance from outhalf David Humphreys produced a perfect start for the home side.
Full back Rhys Williams ran the ball back and appeared in a 70-metre move three times before impressive centre Tom Shanklin took the final pass to score under the posts.
Humphreys replied with a dropped goal, but Ulster let their guard down in the last move of the half to allow Williams to brush off several weak tackles to score a soft try.
The Blues were in again in the opening minutes of the second half when Shanklin snared his second after a break from outhalf Nick Robinson.
Robinson helped the visitors' cause by earning a 54th-minute yellow card for reckless use of the boot, and hard-working prop Best gave visiting fans some hope with a try from a close-range lineout.
Robinson had just returned to the field when his skipper, Martyn Williams, was carded for a professional foul, and Ulster took immediate advantage when replacement back-rower Brosnihan went over the try-line with his first touch of the game.
Humphreys came within inches of the winning try in the 77th minute, but the Blues held on for a crucial win.
A minute's silence was held before the kick-off in the memory of John McCall, the Ulster Schools captain who died during a match at the under-19 World Cup in Durban last week.
CARDIFF BLUES: R Williams; N Walne, T Shanklin, I Harris, J Vaughton; N Robinson, R Powell; J Yapp, R Thomas, B Evans, C Quinnell, J Brownrigg, R Appleyard, M Williams (capt), N Thomas. Replacements: M Allen for Vaughton (40 mins); Sowden-Taylor for Appleyard (76 mins); A Moore for Shanklin (78 mins).
ULSTER: P Wallace; J Topping, S Stewart, P Steinmetz, T Howe; D Humphreys, N Doak; S Best, M Sexton, R Moore, G Longwell, M McCullough, N Best, N McMillan, A Ward (capt). Replacements: P Shields for Sexton, R Frost for Longwell, R McCormack for Moore (all 52 mins); W Brosnihan for N Best (70 mins).
Yellow cards: N Robinson, M Williams (Cardiff Blues)
Referee: Gregg Davies (Scotland)
