Leinster's hopes of making the Pro12 play-offs were all but ended as Ulster moved top of the table with a 26-10 victory on Friday.
After a valiant 25-20 extra-time defeat to Toulon in last weekend's European Champions Cup semi-final, Leinster headed into the Irish derby looking to extend their hopes of silverware this term.
But Matt O'Connor's men fell just short fell short at the Kingspan Stadium.
Leinster made an excellent start when an early Jimmy Gopperth penalty put them in front and when Ben Te'o eluded a tackle to score the visitors were 10-0 ahead.
However, Ulster hit back before the 15-minute mark when Iain Henderson broke through the line to touch down, with Sean O'Brien going into the sin-bin for a dangerous tackle soon after to put Leinster at a numerical disadvantage.
A pair of Ruan Pienaar penalties put Ulster ahead by the break and he added six more points with the boot after half-time to stretch the lead.
The game was put beyond doubt in the 73rd minute when Paddy Jackson set up Pro12's top try scorer Craig Gilroy to go over.
Elsewhere, Edinburgh steamrollered bottom club Zebre 37-0 to climb into the top half.