A brace of tries each from Jimmy O'Brien and Josh Kenny brought Leinster's winless run in the URC to an end as they saw off Scarlets 36-19 at Aviva Stadium.
Leo Cullen's side had lost their previous two games to Cardiff and Glasgow, but his side recovered after a slow start to win this one with a strong second-half showing.
O'Brien and Kenny were two of just three players to hold onto their places after last week's defeat as a raft of Ireland internationals returned to the fold, including Andrew Porter.
Leinster were made to work for their bonus point, with four of their tries coming in the second half, including two in the third quarter for wing O'Brien.
The Welsh side were hamstrung by the first-half yellow cards shown to Joe Roberts and Jarrod Taylor, forcing them to play five minutes with only 13 men.
Captain Fletcher Anderson was outstanding for the Scarlets, who remain third from bottom in the URC table.
The bonus-point win moves the eastern province up to third in the table.
Their recent Scottish-Welsh theme will continue next weekend when they play Edinburgh at the same venue in the Champions Cup last 16.
Additional reporting: PA
