Despite having two players sent to the sin bin in the second half, Leo Cullen's men stood firm in defence and took all their chances to inflict the first defeat of the season on the high flying Blues with a thrilling four try display.
Coach Michael Cheika had warned his side to prepare for an early onslaught from the league leaders and the Blues stole the first line-out from the visitors and forced them to defend desperately in the opening 10 minutes.
Twice the Blues reached the Leinster line only to be knocked back by a superb defensive line expertly marshalled by back row men Shane Jennings and Jamie Heaslip. On the second occasion a Chris Whitaker clearance turned defence into attack and a head high tackle by home skipper Xavier Rush on Trevor Hogan gave Leinster the chance to open the scoring.
It may have been a long shot, from all of 48 metres, but Irish A outside half Jonathan Sexton fancied his chances and made no mistake.
That lead was increased midway through the first-half when Leinster capitalised on a double dose of disasters in the Blues' 22 by Ben Blair and Nick Robinson. They earned Cullen's men a scrum 15 metres out and after Bernard Jackman and Stan Wright had driven even closer it was a long cut out pass from Christian Warner that sent Luke Fitzgerald racing over unopposed in the right corner.
That try proved to the unbeaten home side that they were in for a long battle and their response was immediate. Robinson hit the mark from 45 metres with a penalty and then Blair cut the Leinster defence to shreds with a brilliant sidestepping run to pave the way for a Mark Lewis try that levelled the scores.
That score upped the ante and when the two packs erupted at a scrum 45 metres out the referee had to warn both captains. Leinster won the penalty and Sexton slotted another superb long range goal to regain the lead.
The Blues had their chances to score before half-time, but right wing Jamie Roberts knocked-on in the act of scoring and Robinson was hopelessly wide with a penalty with the final kick of the half.
The first score in the second half was always going to be vital and it fell to the visitors when Sexton kicked across the home 22 and caused enough confusion for Fitzgerald to snap up his second try.
Sexton's conversion extended the lead to 10 points, although two quick-fire penalties from Robinson soon brought the Blues back into contention. That threw the game back into the melting pot and, when Fergus McFadden was sent to the sin bin for killing the ball, it looked as though the Blues might take control.
But instead of making the most of their extra man they conceded two tries in the space of three minutes. A Jackman interception on his 22 turned defence into attack, and eventually a corner try for Heaslip, before Sexton breezed over for the next sucker punch after another home disaster.
Sexton's conversion was the final nail in the Blues' coffin and a late score by Tom James was little consolation.
Cardiff Blues
Tries: M Lewis, T James
Pens: N Robinson (3)
Leinster
Tries: L Fitzgerald (2), J Heaslip, J Sexton
Cons: J Sexton (2)
Pens: J Sexton (2)
Cardiff Blues: B Blair; J Roberts (T Riley 9-16, 41), T Selley, D Hewitt, T James; N Robinson (D Flanagan 66), J Spice (R Rees 60); J Yapp, G Williams, G Powell, R Sidoli (B Davies 65), P Tito, M Lewis (S Morgan 65), R Sowden-Taylor, X Rush (Captain)
Leinster: R Kearney; G Brown, F McFadden, C Warner, L Fitzgerald; J Sexton (R McCarron 78), C Whitaker; S Wright, B Jackman (B Blaney 72), S Knoop (J Gomez 51-56), T Hogan (C Jowitt 65), L Cullen (Captain), K McLaughlin (S Keogh 41, J Gomez 76), S Jennings (K Gleeson 61), J Heaslip
Yellow Cards: Leinster: F McFadden 57; S Wright 76
Referee: Peter Allan (Scotland)
