Expertly directed by fly-half Ceri Sweeney, the Blues did enough to merit this hard-earned win, and denied Leinster a losing bonus point in the end.
They showed commendable enterprise from the start, spreading the ball wide at every opportunity, but it was Leinster who created the first clearcut scoring chance, only for centre Eoin O'Malley to throw his pass out of the reach of unmarked winger Niall Morris and into touch.
At the other end, Blues speedster Richard Mustoe almost sneaked in on the right, but could not prevent a foot landing on the touchline.
In the event, it was a penalty by Sweeney which put the Blues in front, but they spurned further efforts, preferring to go for the close range lineout.
Mustoe was held up just short and number 8 Xavier Rush lost the ball forward as he dived for the line, but the Blues' adventure was finally rewarded when flanker Martyn Williams popped up as a link man on the blindside of a ruck and put full-back Dan Fish in at the corner for an unconverted try.
Leinster hit back in the closing seconds of the first half, full-back Isa Nacewa, who had missed two earlier attempts, slotting over a straightforward penalty.
Encouraged by this, Joe Schmidt's men stepped up the pace after the break, lively fly-half Ian McKinley being foiled by a last-ditch tackle from home scrum half Tom Slater, before the visiting pack drove across the line, but were unable to ground the ball.
The Blues soon regained control, however, with flanker Andries Pretorius increasingly prominent, and Williams darted over only to be called back for a forward pass by Sweeney.
The Blues maintained their pressure, but were unable to turn territory into points, and their lead only survived when Leinster failed to convert a couple of noteworthy try-scoring chances.
Young centre Eamonn Sheridan was held up over the try-line. Soon after, Nacewa switched the direction of play and sent Andrew Conway galloping into the Blues' 22, but the winger's final pass went to ground when flanker Dominic Ryan was up in support.
The inevitable substitutions disrupted the flow, but the introduction of Cook Islands prop Stan Wright, making his first appearance since injuring his Achilles in August, reinforced Leinster scrum.
Sweeney was just off target with a penalty from halfway, but when he had another shot from wide out, he curled the ball inside the far post to clinch the victory for the hosts.
Speaking afterwards, Leinster head coach Joe Schmidt said: "The positives were that there were a few guys making their first starts of the season. Also, we kept trying right to the very end.
"But we've got to maintain our standards and credit to Cardiff because they held on to the ball for long periods. A few more of the (younger) guys also picked up a bit more experience, which will stand to them.
"The fact that we are down 15 players would indicate that this is a difficult time of the year, but it's like that for a number of teams in the league and I know that Cardiff were without a few guys too.
"It was particularly disappointing to lose out on the bonus point at the end. We have to pick ourselves up and resume the scramble for points next weekend."
|Cardiff Blues Score Card|
|Leinster Rugby Score Card|