Leinster (22) 43
Tries: O'Brien, Ryan 2, McFadden, Nacewa, O'Malley Cons:Sexton 5 Pen: Sexton
Saracens (12) 20
Tries: Short, Brown, Mordt Con: Farrell Pen: Farrell
Dominic Ryan dives over for Leinster's second try at the RDS
Leinster ensured their qualification for the quarter-finals of the Heineken Cup by securing a bonus-point win over Saracens at the RDS in Pool Two.
The Irish province led 22-12 at half-time and extended their advantage.
Dominic Ryan (2), Sean O'Brien, Fergus McFadden, Isa Nacewa and Eoin O'Malley were the try-scorers for the home side, with Jonathan Sexton kicking 13 points.
James Short, Kelly Brown and Nils Mordt touched down for Saracens, Owen Farrell adding a penalty and a conversion.
Saracens were only 10 points adrift at half-time, turning around with the advantage of a blustery wind, but tries from McFadden, Nacewa and O'Malley eased Leinster away.
In a free-flowing first half, man-of-the-match O'Brien and Ryan (two) touched down for the hosts, with Short and Brown crossing for Sarries.
But the English Premiership high-flyers were taught an attacking lesson after the break, and an injury-time try from Mordt was meaningless in the end.
The bonus-point victory keeps Leinster five points clear of Clermont Auvergne and guarantees them top spot in Pool Two with a better head-to-head record over the French side.
With the wind at their backs, Leinster moved 12-0 ahead thanks to two early tries.
Brian O'Driscoll and Nacewa created an opening on the left, and the supporting Richardt Strauss put O'Brien over despite the presence of Brown.
There was a further injection of pace in the 12th minute when a wraparound move involving McFadden and Sexton set up Shane Horgan for a run down the right.
Leinster secured quick ball and, from a position close in, passes from O'Brien and Nacewa put 20-year-old flanker Ryan over for a converted try.
Saracens pounced on a Leinster error to run in a settling 24th-minute score.
Gavin Henson is tackled by Jonathan Sexton and Cian Healy
Luke Fitzgerald's sloppy pass near the halfway line was gathered on the bounce by Short, who had the pace to scamper away and touch down by the posts.
Farrell added the conversion, and although Sexton pulled a penalty back after Rhys Gill dropped a scrum, there were more encouraging signs for Sarries.
Brad Barritt got his legs pumping on a huge surge into the Leinster 22, Carlos Nieto rumbled forward on the recycle and a subsequent knock on let Leinster off the hook.
But they could do nothing about the brilliant move which led to Brown's 33rd-minute effort.
Sarries gobbled up Fitzgerald's clearance kick before Schalk Brits roared forward linking with David Strettle, who offloaded for Andy Saull to send Brown over in the right corner.
Farrell failed with the conversion, and, as the open style of rugby continued, Leinster mustered a response before the break.
O'Brien burst past two tacklers and, after a well-managed ruck, Sexton's long pass allowed Shane Jennings to lay off for Ryan to grab his second try.
Sexton tagged on the tricky conversion for a 10-point buffer at half-time, and it was his half-break that ignited Leinster's attack again for their bonus point try.
After soaking up some Sarries pressure, Sexton and O'Driscoll exposed the Sarries defence near halfway, Strauss then took the ball on and McFadden had a comfortable 30-metre run to the line, with Sexton adding the extras.
A Farrell penalty made it 29-15, but another sumptuous score saw Leinster put the result beyond doubt. Sexton, O'Driscoll and O'Brien were involved in a stylish break which finished with Nacewa stepping past Mordt for the try.
Three minutes later, Farrell's missed tackle invited replacement O'Malley through and he jinked his way past the covering Short for a classy seven-pointer.
A raft of substitutions broke up the tempo and after Leinster's Devin Toner saw yellow for collapsing a maul, Sarries salvaged some pride as Barritt put Mordt over for the ninth try of an entertaining European tie.
And the defeat, Saracens' fourth in the pool, was made worse when Gavin Henson, who came on as a replacement, Steve Borthwick, Michael Tagicakibau, Hugh Vyvyan and David Strettle all picking up knocks, with Henson's calf injury looking the most problematic.
Leinster head coach on his side's match against Racing Metro on Friday:
"We know we have to win in Paris to get a quarter-final back home. We will certainly endeavour to do that.
"We have put ourselves into a position now, that we would be crazy not to (go for a win in Paris).
"I'm delighted with where we are and it's about keeping our feet on the ground and not wasting the opportunity that we have got next Friday night in Paris."
Saracens director of rugby Mark McCall:
"We came up against a top quality side who are on top of their game and it has shown us that this competition is pretty unforgiving.
"If you lose concentration for a second, which is what we did in the first half defensively, they have the power runners and quality to score tries.
"We thought at 15-12 with five minutes to go to half-time, with the wind at our backs in the second half, we were in a decent position - but unfortunately we were a bit naive.
"In some ways, we are a relatively new Heineken Cup team and this whole experience in this pool has been one of learning for us. It shows us we are not where we want to be."
Leinster: I Nacewa; S Horgan, B O'Driscoll, F McFadden, L Fitzgerald; J Sexton, E Reddan; C Healy, R Strauss, M Ross; L Cullen (capt), N Hines; D Ryan, S Jennings, S O'Brien.
Replacements: J Harris-Wright for Strauss (67), H van der Merwe for Healy (67), C Newland for Ross (67), D Toner for Hines (61), K McLaughlin for Jennings (67), I Boss for Reddan (67), I Madigan for Sexton (70), E O'Malley for Horgan (61).
Saracens: N Mordt, D Strettle, M Tagicakibau, B Barritt, J Short, O Farrell, R Wigglesworth, R Gill, S Brits, C Nieto, S Borthwick, H Vyvyan, K Brown, A Saull, E Joubert.
Replacements: J George for Brits (67), J Saunders for Henson (68), P Du Plessis for Nieto (61), H Smith for Vyvyan (40), J Melck for Saull (53), N de Kock for Wigglesworth (53), G Henson for Tagicakibau (35), N Cato for Strettle (65)
Referee: Romain Poite (France).