Leinster's late push for a fourth try looked to be in vain but Keogh was able to scamper over in deepest injury-time, after Ulster had lost Robbie Diack to the sin-bin.

That score has closed Munster's lead at the top of the table back to three points, ahead of Leinster's crunch trip to Thomond Park next Saturday.

Michael Cheika's men were full value for this win and two tries in the space of four minutes, from Fergus McFadden and Leo Cullen, set them on the road to their seventh straight league success.

The rampaging Rocky Elsom added another, 13 minutes from the finish, and with Ulster's defence tiring at the finish, Keogh sliced through for the all-important fourth try.

With three of Ireland's Grand Slam winners in their side - Paddy Wallace, Tom Court and Rory Best - Ulster travelled south with confidence and they would have been heartened by a scoreless opening quarter.

Court and Wallace got ball in hand early on but Leinster looked the sharper side and Contepomi was narrowly off target with a ninth-minute penalty chance.

David Pollock and Chris Henry engineered a drop goal shot for Ian Humphreys but he snatched at it and the Ulster out-half also missed a long range penalty after ruck interference from Shane Jennings.

With both defences fanning out across the pitch and little space for either team to manoeuvre in, it was left to Contepomi to open the scoring with a 20th-minute penalty.

Andrew Trimble, a player who failed to feature in Ireland's Grand Slam run, took a beautiful line on 25 minutes and darted menacingly through the Leinster midfield, but his attempted chip over Shane Horgan was easily caught by his wing rival.

Horgan, who was also unused during the RBS 6 Nations, was released down the right wing soon after and a quick switch of direction almost had Bernard Jackman bulldozing over in the left corner.

But neither side could conjure up a try before half-time and two successful penalties from Humphreys and Contepomi left Leinster 6-3 ahead at the break.

Gordon D'Arcy, straight back into league action after the Grand Slam, helped Leinster find an extra gear on the restart.

He made a brilliant break out of his 22 to set his centre partner McFadden up for a 40-metre dash to the left corner, with Contepomi adding the conversion.

On 53 minutes, Leinster's forwards rumbled on and Cullen barged past Ian Humphreys to score his first try for Leinster since the 2004/05 season.

With Humphreys off the pitch, Clinton Schifcofske clawed back some of the difference for Ulster with a well-struck penalty.

However, Leinster were punching more and more holes in the Ulster defence and after an excellent turnover by Jennings, Isa Nacewa and Horgan combined to set up man-of-the-match Elsom for a breakaway third try.

Wallace and Cillian Willis tried to inspire a revival from the visitors but Leinster always looked capable of scoring another try and it duly came from Keogh, after Chris Whitaker had released him off a scrum.