Leinster rallied in the second half to beat Ulster 24-12 in Dublin on Friday as they ended their Irish rivals' unbeaten start to the Pro14 season.
Ireland internationals Sean Cronin and Robbie Henshaw both scored tries for Leinster as the hosts, who have games in hand over Conference A leaders Ulster, closed the gap at the top of the table to five points.
Ulster, who kicked off on a run of 10 straight wins, saw John Cooney kick three penalties - two while Marcell Coetzee was in the sin-bin - to establish a 9-5 lead.
But Cronin and Henshaw's efforts, allied to Dave Kearney's earlier try, saw Leinster bounce back from last week's shock defeat by Connacht.
James Tracy's clinching try seven minutes from time came soon after Cooney's fourth penalty of the match.