Leinster rounded off the league phase of the RaboDirect Pro12 with a bonus point 37-19 win as the Ospreys relinquished their grip on the trophy.
The Welsh region stunned the home support when they won a dramatic final at the RDS last May, but they were unable to repeat the feat on a rain-soaked night in Dublin.
A brace of Andrew Conway tries catapulted Joe Schmidt's men into a 14-0 lead, but Dan Biggar and Ben John replied as the Ospreys cut the gap to two points. Jonathan Sexton landed an injury-time penalty to give the hosts a 17-12 interval lead, and Conway's hat-trick score further strengthened their hand.
Sexton popped over two more penalties, either side of a Tom Isaacs try, before Cian Healy came off the bench to run in the province's fourth touchdown late on.
Having lost the last three league deciders, Leinster have unfinished business with the Pro12 play-offs and they will entertain third-placed Glasgow Warriors at the RDS next Saturday.