|Leinster (8) 8|
|Try: Cronin Pen: Sexton|
|Ulster (3) 3|
Ulster failed to break Leinster's firm defence and slipped to a disappointing Pro12 derby defeat at the RDS.
Sean Cronin's 37th-minute try was the difference between the teams in a dour game dominated by defences.
Jonny Sexton and Paddy Jackson traded penalties with Leinster leading 8-3 at the interval, and neither side scored in a slow-paced second half.
Ulster had their best spell late in the game and despite a losing bonus point dropped down to seventh in the table.
Both sides were under pressure for a victory after poor results in the European Champions Cup.
Leinster, coming off back-to-back defeats to Wasps and Bath, started brightly in front of a sparse home crowd with Sexton nailing a sixth-minute penalty to put his side 3-0 up.
Paddy Jackson missed a simple penalty attempt three minutes later but converted a more difficult effort from nearer the sideline to level the scores after 14 minutes.
Leinster make the breakthrough
Leinster dominated possession and showed their intent when Sexton turned down easy points in favour of a kick to the corner.
Leo Cullen's side had a number of attacking lineouts in the second quarter, with Robbie Diack stealing Sean Cronin's throw as Ulster's defence held firm.
Eventually the pressure told with Cronin rumbling over from close range in the 37th minute after another lineout.
Ulster failed to commit enough bodies to the maul and Cronin crossed to put Leinster 8-3 ahead, Sexton missing the conversion.
Leinster found another gear after the restart and went close to breaching their Irish rivals' defence for a second time.
Rhys Ruddock made a great break straight through Ulster's porous midfield and when the ball was recycled to Sexton, his fast past was fumbled by Ben Te'o with the try line at his mercy.
It was a let-off for Les Kiss' side and in the 49th minute, Rory Best held up Josh van der Flier on the line to keep Leinster at bay.
Ulster squander rare opportunity
Ulster's strike runners were starved of possession but Andrew Trimble made one penetrating break to put the visitors into the Leinster half for the first time in the second period.
Pienaar turned down a penalty as Ulster went looking for a try, but after going through several phases Diack conceded a penalty allowing the home side to clear.
Leinster dictated the pace of the game but Ian Madigan missed a drop-goal attempt as the home side struggled to put Ulster away.
Ulster: P Nelson; A Trimble, D Cave, S McCloskey, C Gilroy; P Jackson, R Pienaar; K McCall, R Best (capt), W Herbst, I Henderson, D Tuohy; R Diack, S Reidy, N Williams.
Replacements: C Henry for Reidy (43), R Lutton for Herbst (55), R Wilson for Diack (61), P Marshall for Pienaar (74), L Ludik for McCloskey (74), R Herring for Best (76).
Leinster: I Nacewa; Z Kirchner, B Te'o, I Madigan, L Fitzgerald; J Sexton, L McGrath; J McGrath, S Cronin, T Furlong; D Toner, M McCarthy; R Ruddock, J van der Flier, J Heaslip (capt).
Replacements: E Reddan for L McGrath (32) M Moore for Furlong (51), J Tracy for Cronin (60), P Dooley for J McGrath (60), R Molony for McCarthy (67), N Reid for Sexton (67), G Ringrose for Reid (73).