An early second-half blitz when Leinster were down to 14 men left last year's Celtic League champions on the verge of crashing out of this season's competition.

Fly-half Iestyn Harris, whose 20 points took him past 250 in 23 matches for Cardiff, made sure of the Welsh side's first home win of the campaign.

Despite Leinster's efforts to spread the ball, the first-half was a shapeless affair, marked by some aimless kicking and the constant blast of Scottish referee Iain Ramage's whistle.

Towards the break, the home side's talismanic Canadian back row, Dan Baugh, began to batter holes in the Irish defence and South African full-back Donavan van Vuuren came close to a debut try.

Leinster prop Niall Treston was sin-binned just before half-time and was still absent as Cardiff rattled 15 points in the opening exchanges of the second period.

A brilliant over-arm pass by skipper Martyn Williams in midfield allowed left-wing Anthony Sullivan to dive in at the corner.

Then it was livewire flanker Williams who won a turn over on the halfway line and, after a darting run by scrum-half Ryan Powell, popped up to finish the move with a well-deserved touchdown.

Leinster were far from finished and centre David Quinlan grabbed a loose ball in the Cardiff 22 to put lock Aidan Kearney over.

But the holders were unable to maintain the pressure and Harris' boot had the final say.

Cardiff: Donavan van Vuuren; Nick Walne, Jamie Robinson, Pieter Muller, Anthony Sullivan; Iestyn Harris, Ryan Powell; Tim Payne, Greg Woods, Gary Powell, Heino Senekal, Adam Jones, Rob Appleyard, Martyn Williams (capt), Dan Baugh.
Reps: Kenneth Fourie, Andrew Lewis, Luke Tait, Dan McShane, Richard Smith, Nick Robinson, Rhys Williams.

Leinster: Christian Warner; Kieran Lewis, Shane Horgan, David Quinlan, Gordon D'Arcy; Andy Dunne, Brian O'Meara; Emmett Byrne, Peter Smyth (capt), Niall Treston, Ben Gissing, Aidan Kearney, Aidan McCullen, Liam Toland, Des Dillon.
Reps: Peter Coyle, Gavin Hickie, Shane Jennings, Niall Breslin, Ben Willis, Matthew Leek, John McWeeney.

Referee: Iain Ramage (Scotland).