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.