Conor O'Shea hailed his Harlequins after they became the second side in 16 years to win a European tie at Thomond Park. First-half tries from the lock George Robson and scrum-half Danny Care sent the English club into the Amlin Challenge Cup final, in which they will face Stade Français in Cardiff on 20 May.
Munster rallied through tries from Felix Jones and Doug Howlett but the Irish province lost a fourth semi-final in a row. Even a red card for the England No 8, Nick Easter, with 10 minutes left – for a second yellow – could not stop Quins, who followed Leicester (in 2006) in beating the Red Army in Limerick.
O'Shea, their director of rugby, said: "I could not be prouder of the boys. I always believed we had that sort of performance in us. This proves that we can deliver on the big occasion and now we have a shot at silverware and qualifying for next season's Heineken Cup. It's from wins like this that we can move the club forward."
Easter had said that a victory here would be the "biggest" result in Quins' 145-year history, and they began with attacking intent which was rewarded by Robson's ninth-minute try. The wing Gonzalo Camacho beat Paul Warwick and Howlett down the left and as Munster struggled to regroup the ball was worked across the field for Robson to crash over. Nick Evans kicked the conversion but the New Zealand fly-half was off-colour and he missed penalties on 26 and 28 minutes.
Evans had picked up a knee injury and the full-back, Mike Brown, took over temporarily at No 10. He was held up short of the line and after Evans showed courage to go close, Care burrowed over. The television match official said he had enough downward pressure on the ball.
Munster scored seconds before half-time, when Jones took Warwick's pass to touch down, and Ronan O'Gara's conversion reduced the deficit to seven at the break. The home side brought on Paul O'Connell but Romain Poite then sent his second-row partner, Donncha O'Callaghan, and Easter to the sin-bin following a scuffle on the floor. That allowed Rory Clegg to kick a 49th-minute penalty and the replacement fly-half kicked another shortly before the hour.
Poite disallowed two tries for forward passes before Easter was dismissed for his second offence of the half, this time diving in at the side of a ruck. Howlett scored with seconds remaining.
O'Shea said: "We knew we'd have to ride our luck at times but when Chris [Robshaw] won the toss and opted to play into the wind, that showed the belief in the side. The talk during the week was that we would come over here, roll over and have our tummies tickled but that was never going to happen. We would not be cowards. The players deserve to celebrate tonight."
Munster's coach, Tony McGahan, said: "We were terribly disappointing but full credit to Harlequins. They had a game plan, were outstanding at the breakdown and in defence and deserved the win. Does that make Harlequins favourites against Stade Français? They have certainly got a great opportunity if they play with the same spirit and execution as they did against us."
Munster F Jones; D Howlett, L Mafi, P Warwick (S Tuitupou, 40), K Earls (J Murphy, 64); R O'Gara (capt), C Murray (P Stringer, 56); W du Preez (M Horan, 56), D Varley (M Sherry, 73), T Buckley (J Hayes, 40), D O'Callaghan (D Ryan, 68), M O'Driscoll (P O'Connell, 40), D Leamy, J Coughlan, D Wallace.
Harlequins M Brown; G Camacho, G Lowe, J Turner-Hall, U Monye; N Evans (R Clegg, 40), D Care; J Marler (C Jones, 65), J Gray, J Johnston, O Kohn (T Vallejos-Cinalli, 72), G Robson, M Fa'asavalu, N Easter, C Robshaw (capt).
Referee R Poite (France).
Tries: Jones, Howlett
Tries: Robson, Care
Cons: Evans, Care
Pens: Clegg 2