Leinster took the lead in the first minute, David Quinlan gathering Felipe Contepomi’s chip ahead to gallop towards the line and touch down under the posts.
Contepomi’s conversion was successful, and the fly half added another 3 points twenty minutes later when Blues were penalised for pulling down at the lineout.
For first 35 minute Lienster played most of the rugby in Cardiff’s half, it took that long for Blues to get points on the board, Lee Thomas slotting over a difficult penalty in poor conditions from the 40 metre line.
Cardiff’s best chance of the half came in injury time; Shane Byrne, who had a bad night with his aim, overthrew into a line out and Martyn Williams collected the ball unopposed at the back. However Blues could not take advantage of their situation and at the break the score remained 3-10.
In the second half the tempo of the game picked up and Blues were the first to add points through a second Lee Thomas penalty. But despite a sustained attack started by scrum half Ran Powell in his own 22, Blues were unable to add to their total.
It was left to a late try by Leinster full back Girvan Dempsey from a break by replacement Gordon D’Arcy to secure the victory for the visitors and deny Cardiff even a losing bonus point in the process.