Leinster moved level on points with Munster atop the Pro12 table after running in 10 tries including a hat-trick for Rory O'Loughlin in a 70-6 thrashing of Zebre on Friday.
Jonathan Sexton skippered Leinster on his return to action, having not featured since picking up a hamstring injury for Ireland against New Zealand in November.
The fly-half played a little over an hour, kicking 12 points as the hosts romped to victory while Zebre prop up the table having won just one of their 11 matches.
The clash went very much to form, Leinster going into the break 35-6 up and with a bonus point already safely secure thanks to scores from Sean O'Brien, Hayden Triggs, Luke McGrath, Cian Healy and O'Loughlin.
Garry Ringrose added a sixth after the resumption, O'Loughlin going over twice in quick succession to complete his treble before Ringrose doubled his tally and Jamie Heaslip capped a miserable outing for sorry Zebre.
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It was a much more tightly contested affair between Scarlets and Ulster, the Welsh outfit just edging it 16-13 after a second-half fightback.
Scarlets trailed 13-6 at the interval, Jacob Stockdale's try and the boot of Paddy Jackson doing the damage for Ulster.
Dan Jones' third penalty cut the deficit to four, and Scarlets forged ahead when Sean Reidy was sin-binned for a high tackle, the hosts awarded a penalty try with Jones adding the extras, leaving Ulster to settle for a losing bonus point.
Jones was filling the void left by Rhys Patchell, whose three-month absence due to an ankle injury was confirmed on Friday - ruling him out of Six Nations contention.
Friday's other encounter saw Newport Gwent Dragons run out 26-8 victors at home to Treviso.