Munster saw off Leinster 34-23 in front of a bumper crowd at the Aviva Stadium in Dublin.
Criticised for their early-season form under new head coach Anthony Foley, Munster produced the ideal response with a storming forwards-dominated display that had the hallmarks of Foley's own playing days. They even survived four yellow cards in the second half to seal a deserved derby victory 34-23 - led by 21-point hero Ian Keatley and man of the match Conor Murray alongside him at half-back.
James Cronin and Robin Copeland both crossed for tries, with Ian Keatley adding an intercept effort as the visitors moved 28-9 clear for half-time. Ian Madigan kicked Leinster's points from penalties. In front of a 43,817-strong crowd, the Reds continued to outsmart the reigning Guinness PRO12 champions until that succession of sin-binnings saw Leinster come back into contention.
Munster lost their discipline as Darragh Fanning swept through for a try and David Foley pulled down a maul for a Leinster penalty try. That cut the gap to 31-23 but Keatley's replacement JJ Hanrahan settled the issue with a 76th-minute penalty.
It was Leinster's first ever PRO12 loss at either Lansdowne Road or the Aviva Stadium, ending a run of 13 victories, and a sizeable blow to their league title defence. Leinster head coach Matt O'Connor was forced into a couple of late changes, with Jack McGrath (calf) and Rob Kearney (back) making way for Michael Bent and Brendan Macken respectively and Madigan moving to full-back. Further injuries to Fergus McFadden and front-row replacement Tadhg Furlong stretched the Leinster squad and prevented them from mustering much of a comeback.
James Cronin brought the first scrum down, allowing Madigan to clip over the opening points from the left. However, Dominic Ryan gave away a cheap penalty which saw Keatley level from 42 metres out. Mike Ross got the edge on Cronin again in a scrum, setting up Madigan's second penalty - this time from a more central position - before Munster built some momentum at the other end.
Murray was held up by Eoin Reddan after a rousing set of phases from Foley's charges, who equalised courtesy of a second Keatley penalty in the 16th minute. Even better followed for the visitors as Andrew Conway wrestled possession back for the Reds, the dynamic Denis Hurley punched it up in midfield and three covering defenders were unable to prevent prop Cronin from stretching over for a try.
Keatley missed the conversion but was successful with a penalty as Munster turned the screw in the scrum. They also realigned well to recover from a Jimmy Gopperth midfield break. However, the Leinster defence was coming under sustained pressure from Munster's very effective 'pick and drive' game and number eight Copeland crowned his first inter-provincial appearance with a seven-pointer under the posts.
A long lineout throw over the back to Devin Toner led to a Madigan penalty approaching half-time, but Leinster were stung by Keatley's try which saw him intercept Gopperth's attempted inside pass and race away from just inside the Munster half. Keatley miscued a long-range penalty on the resumption and Paul O'Connell and company were soon held up over the Leinster line as Munster hunted for the bonus-point score.
Hooker Sean Cronin led the Leinster response with some lung-bursting carries - the most promising of which was spoiled by a knock-on out wide on the right. Amid a scrappy spell, the penalties began to stack up against Munster and referee Ian Davies lost his patience as Damien Varley was sin-binned for a cynical offside.
Fellow replacement front rower BJ Botha followed him off the pitch just two minutes later, having infringed at a midfield ruck, and suddenly Leinster had a two-man advantage. The hosts kicked for the corner and winger Fanning hared onto Gopperth's inviting short pass, with his diagonal run taking him away from Simon Zebo to score by the posts. Madigan converted for 28-16.
A Keatley three-pointer kept Munster on course, though, with fit-again captain Peter O'Mahony now on the pitch. Shortly after Varley's return, lock Foley was shown yellow for collapsing a Leinster maul as it powered towards the try-line, and the resulting penalty try was converted by Madigan. Munster showed their mettle by setting up Hanrahan for what proved to be the clinching penalty and, despite losing Murray late on, they defended manfully to deny Leinster a losing bonus point.