With just four points between the sides at half time, it looked like the hosts would again struggle to see off the Welsh visitors, after last season’s 22-21 win, but the Leinster bench provided plenty of spark, and tries from supersubs Sean Cronin, Barry Daly and Nick McCarthy did the damage.
It was Leinster’s 13th win in a row over the Blues as they got back to winning ways at the RDS, after last May’s Guinness Pro12 playoff semi-final defeat to Scarlets.
After a sombre minute’s silence for the late Willie Duggan, the game took a while to warm up, with a scrappy start seeing unforced errors by both sides, including Leinster’s loss of a lineout inside the Cardiff 22.
Ross Byrne then missed a relatively easy penalty as the opening 10 minutes passed, but Steve Shingler made no mistake on 15 with his kick giving the visitors an early lead on their first push into Leinster territory.
The visitors were enjoying the better of play now, and they looked set to increase their dominance when Isa Nacewa was sin binned for a high tackle on Alex Cuthbert.
The referee asked for a replay on the big screen, but there were no doubts and the Fijian received his fifth yellow card in a Leinster shirt.
A break from Reynold Lee-Lo cut Leinster open seconds later, with Rob Kearney delivering a big tackle to stop the onslaught.
Shingler kicked a second penalty after Cardiff dominated the Leinster scrum, to put six points between the sides.
With Nacewa still in the bin, Leinster enjoyed their best spell of territory and possession, and such was their confidence, Byrne turned down the easy three points in favour of a lineout five yards from the Cardiff line.
Tracy hit Ruddock with the dart, then attached himself to the back of the maul, and eventually touched down.
Byrne added the extras and with Nacewa back on seconds later, Leinster had outscored Blues 7-3 while a man down.
Josh Navidi was lucky to avoid a yellow card when he caught Nacewa around the neck on the cusp of half time, but Byrne’s penalty put Leinster 10-6 ahead at the break.
Rob Kearney hobbled off the park just before the break and Barry Daly emerged in the No 23 shirt, with Jordan Larmour switched to full back.
Shingler and Byrne swapped penalties inside the opening five minutes, with Byrne’s penalty smacking off both posts before eventually crossing the bar.
The game still looked in the balance at this stage, but it was all to be turned on its head in a matter of minutes.
Cronin raced home to score his first try of the season after a solid bit of breakdown work by Scott Fardy, who ripped the ball from Blues’ hands to give the replacement hooker a clean run to the line.
That had the crowd on its feet, but better was to come.
Byrne’s cross-field kick was aimed toward Barry Daly, but the winger had plenty to do. He rose, caught the ball one handed, and landed with it in his chest. Suddenly the bonus point was in view.
The fourth try of the night was as impressive as it was unexpected, with the ball flung at pace through almost half the team before sub Nick McCarthy slid home.
Tries: Tracy (32) Cronin (68), Daly (74), McCarthy (76) , Cons: Byrne (34, 69, 74, 76) , Pens: Byrne (40, 45, 60)
Tries: , Cons: , Pens: Shingler (16, 27, 42)
R Kearney (rep: B Daly, 40); A Byrne, R O’Loughlin, I Nacewa (c), J Larmour; R Byrne, L McGrath (McCarthy., ; C Healy (rep: Byrne, 52), J Tracy (rep: Cronin, 52), M Bent (rep: Porter, 52), D Toner, S Fardy (rep: Kearney, 73), R Ruddock (rep: Leavy, 58), J van der Flier, J Conan.
R Williams (Rep: Morgan, 71); A Cuthbert, G Smith, R Lee-Lo, T James; S Shingler (rep: Evans, 70), L Williams (T Williams, 70); R Gill (rep: Domachowski, 57), M Rees (c) (rep: Myhill, 61), K Assiratti (rep: Lewis, 57), S Davies, D Welch (rep: Down, 64), M Cook (rep: Bennett, 75), J Navidi, J Turnbull.
Edinburgh 35 Newport Gwent D’gons 18