Ulster slipped off the top of the Celtic League as Leinster recorded their sixth consecutive victory at a rain-lashed Donnybrook on Friday night.
Leinster (22 ) 32
Tries: Contepomi, Costello
Cons: O'Meara 2
Pens: O'Meara 6
Ulster (16 ) 30
Tries: Howe, Steinmetz, Humphreys
Cons: Humphreys 3
Pens: Humphreys 3
It was Ulster's third defeat in the league this term and all have been away from home.
Leinster, whose winning run followed four opening league defeats, deserved their success although there were only two points in it at the end.
Ulster, newly-crowned Celtic Cup holders, got a couple of late tries to secure a vital bonus point, but it was a flattering scoreline.
Leinster edged ahead in the first half with three penalties by scrum-half Brian O'Meara, David Humphreys replying with one for Ulster.
Then on 22 minutes Leinster got the first try, scored by Argentinian Felipe Contepomi who had come into the Lions line-up in place of the injured Brian O'Driscoll.
Humphreys and O'Meara exchanged penalties to make it 19-6 to Leinster.
Ulster hauled temselves back into contention with a try scored by international winger Tyrone Howe, created by a good break by Paul Steinmetz.
Penalties were exchanged again, leaving the half-time score 22-16.
O'Meara added his sixth penalty of the match in the second half before Victor Costello pounced for what turned out to be a match-winning score.
Ulster full-back Paddy Wallace was caught in possession and from the resulting ruck the Irish international number eight barged his way over. O'Meara's conversion 32-16.
Steinmetz and Humphreys scored tries late on, both coverted by Humphreys but the northern province ran out of time.
Leinster: D'arcy, McWeeney, Contepomi, Quinlan, Burke, Leek,
O'Meara, Corrigan, S. Byrne, Coyle, O'Kelly, Gissing, McCullen,
Replacements: Moran, G. Hickie, Dillon, Kearney, O'Riordan,
Ulster: P Wallace; J Topping; A Larkin, P Steinmetz, T Howe; D Humphreys, N Doak; R Kempson, M Sexton, S Best, R Frost, M Mustchin, A Ward (capt), N Best, R Wilson.
Replacements: P Shields, R Moore, M McCullough, W Brosnihan, K Campbell, S Mallon, B Cunningham.
Referee: Nigel Owens (Wales).