Pro12: Leinster 37-19 Ospreys
Leinster (17) 37
- Conway (3), Healy
- Sexton (3), Madigan
- Sexton (3)
Ospreys (12) 19
- Biggar, John, Isaacs
- Biggar (2)
Andrew Conway's hat-trick secured a home Pro12 semi-final for Leinster and ended Ospreys' faint hopes of forcing their way into the play-offs.
Conway crossed twice in the opening 23 minutes, but Ospreys responded with tries from Dan Biggar and Ben John to trail 14-12 at the break.
Wing Conway added his third try, and despite Ashley Beck's response, Cian Healy had the last word for Leinster.
The Irish province will now face Glasgow in Dublin in the semi-finals.
Reigning champions Ospreys needed a victory to have any hope of snatching fourth place from Welsh rivals Scarlets, but it proved a bridge too far against a slick Leinster outfit, who finish the regular season in second place in the table.
The home side, still bouncing from their Amlin Challenge Cup semi-final thrashing of Biarritz six days ago, quickly set the tone for an open and attacking encounter.
Sharp passing and inventive running angles immediately put the league's meanest defence on the back foot, resulting in two early Conway tries.
Both scores, though, should have been prevented.
Ospreys wing Ross Jones was culpable for the first after just seven minutes, allowing Fergus McFadden's grubber kick to slip through his fingers and legs near the right touchline.
Conway picked up the loose ball and had a clear run to the line. Sexton converted superbly.
Ospreys prop Adam Jones, one of five from the Welsh region named in the Lions squad this week, was the next to be found wanting defensively.
His soft tackle at the base of a lineout out allowed Leinster scrum-half Luke McGrath to break clear, and Conway was perfectly placed on his shoulder to take an inside pass to race in for a second score.
Sexton's conversion completed a breathless opening for the rampant home side, but Ospreys were in no mood to relinquish their hold on the league title without a fight.
Biggar took it upon himself to start the comeback, catching the home defence dozing with a quick tap penalty.
The fly-half had some way to go, but some more weak tackling, notably from McGrath, allowed him to wriggle his way over. He added the extras from the left touchline.
A second try soon followed as Ospreys showed they had the handling skills and dynamic runners to match their host.
A deflected clearance kick fell invitingly for Tom Habberfield and he promptly glided through the serrated defence into Leinster's 22.
Quick ball was secured from the ruck and centre Ben John had too much power for Sexton in the right corner after Tom Bearman's well-timed pass.
But three minutes either side of half-time reasserted Leinster's dominance as they established a 12-point lead that they never looked like relinquishing.
After Sexton's penalty with the final kick before the break, Conway gave the hosts the perfect start to the second half by completing his hat-trick.
Again, wing Ross Jones was caught out defensively as his opposite number collected his own kick ahead far too easily. Sexton's conversion from the right touchline went over off the left-hand post.
A second Sexton penalty extended the lead, but again Ospreys showed a commendable appetite to fight back as they sensed their grip on the title slipping away.
A marginal forward pass call denied Ashley Beck a try under the posts, but the centre's long pass then found Tom Isaacs in acres of space to cross over unopposed, with Biggar converting.
But any thoughts an unlikely late comeback were soon banished by Sexton's penalty and then replacement prop Healy produced a fitting finale to a enthralling contest by sprinting clear for the home side's fourth converted try.
Leinster: R. Kearney; Conway, McFadden, Madigan, Nacewa; J. Sexton, J. McGrath, L. McGrath, Cronin, Hagan, Cullen, Roux, Ruddock, Jennings, O'Brien.
Replacements: Goodman for Nacewa (79), Healy for J. McGrath (62), Cooney for L. McGrath (62), Strauss for Cronin (62), Bent for Hagan (68), Toner for Cullen (68), Murphy for Jennings (58).
Not Used: O'Driscoll.
Ospreys: Fussell; Haberfield, Beck, John, R. Jones; Biggar, Webb; D. Jones, Baldwin, A. Jones, A. Jones, King, Tipuric, Lewis, Bearman.
Replacements: Morgan for Fussell (70), Isaacs for R. Jones (56), Spratt for Webb (16), Bevington for D. Jones (47), Arhip for A. Jones (60), Allen for Bearman (70).
Not Used: Griffiths, Evans.
Referee: Nigel Owens (WRU)
Assistant Referees: Mark Patton, Stuart Gaffikin (both IRFU)
Citing Commissioner: Eugene Ryan (IRFU)
TMO: Alan Rogan (IRFU)