Ulster beat Leinster on Friday night to set up a potential Celtic League decider against Llanelli Scarlets on Friday 14 May.
Ulster (18) 28
Tries: Howe 2, Humphreys
Cons: Humphreys 2
Pens: Humphreys 3
Leinster (6) 6
Pens: O'Meara 2
Llanelli face the Ospreys on Sunday and victory will mean a crucial clash with title rivals Ulster at Stradey Park.
In coach Alan Solomons' farewell game at Ravenhill, Ulster winger Tyrone Howe scored the only two tries of the first half to secure an 18-6 interval lead.
Fly-half David Humphreys got a third try in the second period.
But Ulster could not get a fourth try to earn a precious bonus point.
It means they are joined at the top of the league by Gwent Dragons with Llanelli three points behind with a game in hand.
The Dragons finish with an away game against Leinster which has been switched from Donnybrook to Lansdowne Road.
"I think Leinster can beat Gwent if they show the same commitment they did against us," said coach Solomons.
"As for tonight, I felt it was a magnificent performance from the whole team. The pack was immense."
Leinster's Brian O'Meara got the visitors' points with two penalties.
Skipper Andy Ward, winning his 100th cap for Ulster, was involved in the move for the opening 12th minute try with Neil Doak moving it quickly to the blindside for Howe to smash over in the left corner.
Howe got another try on 28 minutes after Ulster's Humphreys created the chance with a low
cross kick over the Leinster line.
Humphreys added a penalty to extend the lead to 18-6 at the break.
Five minutes after the restart, Humphreys slotted his third penalty to take it to 21-6 for the home side.
The excellent Ulster fly-half crossed for the home side's third try and converted his own
66th-minute score for 28-6.
Ulster: Cunningham, S. Young, Mallon, Stewart, Howe, Humphreys,
Doak, S. Best, Sexton, Moore, Mustchin, Frost, Ward, N. Best,
Replacements: Shields, McCormack, Barker, McMillan, Campbell,
Leinster: Norton, McWeeney, Hearty, Contepomi, Burke, Leek,
O'Meara, Corrigan, S. Byrne, Coyle, Cullen, O'Kelly, Miller,
Replacements: E. Byrne, D. Blaney, Gissing, Dillon, Ronan,
Referee: Nigel Williams (Wales)