Yet within 20 minutes of the re-start they had not only got on level terms, but then edged ahead. It was a remarkable turn-around than stung Leinster into a strong rearguard action that eventually saw them deliver to new coach Joe Schmidt his first competitive win 34-23.
Leinster threatened to blow the Blues away with their fast start, which saw them notch 14 points in 10 minutes. Shane Jennings surged over the line for a try within four minutes and then Isa Nacewa followed suit five minutes later
The power of the home pack put the Blues pack to the sword in the early exchanges and just before the break Young had to bring on experienced prop Tau Filise in place of Tom Davies to shore up his front row.
Davies, making his first Magners League start after his summer transfer from Doncaster Knights, was penalised five times for collapsing the scrum and without a solid platform the Blues simply couldn't function.
Leinster took full advantage of their dominance and as well as those two tries, both of which Nacewa converted, they also turned the screw with two penalties from their Fijian winger to build that 14 point interval lead.
But the Blues hit back with tries from Bradley Davies and Richie Rees and Parks' boot pushed them into a three point lead on the hour.
As the 16,000 home crowd got more and more restless, so Leinster went back to basics up front and finally generated enough forward power to create chances for Fergus McFadden and Ian Madigan to cross.
Those tries not only delivered victory, but also clinched a bonus point and denied the Blues anything.
Scorers: Leinster: Tries: S Jennings, I Nacewa, F McFadden, I Madigan; Cons: I Nacewa 4; Pens: I Nacewa 2. Cardiff Blues: Tries: B Davies, R Rees; Cons: D Parks 2; Pens: D Parks 3.
Leinster: Luke Fitzgerald; Shane Horgan, Brian O'Driscoll (Eoin O'Malley 62), Fergus McFadden (B O'Driscoll 74), Isa Nacewa; Ian Madigan, Isaac Boss (Eoin Reddan 53); Heinke van der Merwe (C Healy 61), Richardt Strauss (John Fogarty 55), Mike Ross (Simon Shawe 67), Nathan Hines, Ed O'Donoghue (Mariano Galarza 78), Sean O'Brien, Shane Jennings (capt, Dominic Ryan 61), Jamie Heaslip.
Cardiff Blues: Chris Czekaj; Richard Mustoe, Casey Laulala, Dafydd Hewitt (Gavin Evans 55, D Hewitt 61), Tom James; Dan Parks, Richie Rees; Tom Davies 3 (Fa'ao Filise 39), T Rhys Thomas, Scott Andrews (John Yapp 49), Bradley Davies, Deiniol Jones (James Down 58), Michael Paterson (Ben White 71), Sam Warburton, Xavier Rush