Munster will travel to France to face Clermont in the Heineken Cup semis after battling past Harlequins 18-12.
Like Saracens on Saturday, this was a result built on gritty defence and big hearts as their second-half showing saw the English have no answer.
Munster will head to the 32,000-capacity Stade de la Mosson in the Languedoc region on April 27.
The contest was played on a firm surface but that did not create an attack-minded first period as both Quins and Munster struggled to threaten.
Conor O'Shea's charges did, however, start the stronger when from the outset Ugo Monye jumped to collect fly-half Nick Evans' kick-off from Paul O'Connell's grasp. That effort led to improving inside centre Tom Casson grubbering to the corner and Munster wing Denis Hurley seemingly looking to have slapped the ball out into touch. Referee Jerome Garces and his assistant failed to spot this act but soon after Quins were on the board when Evans converted a scrum penalty.
Ronan O'Gara, who made his Heineken Cup debut against the likes of Harlequins old boys Will Carling and Thierry Lacroix, missed his first shot at goal, hitting the upright immediately after playmaker Evans had opened matters. Meanwhile, fellow veteran O'Connell was playing like a man possessed at the Stoop.
British and Irish Lions head coach Warren Gatland was watching at the venue and would have taken note of O'Connell and Peter O'Mahony's showings. But despite individual efforts, the Irish were 0-6 down when Evans slotted on nineteen minutes after the tackler failed to roll away. Things were made worse when O'Gara missed off the tee again soon after.
Munster though were beginning to take a stranglehold on the game - a trend that kicked into life in the second 40 - and when Casey Laulala made good metres on 25 minutes, a penalty soon arrived for O'Gara that he converted. As was expected, scoring chances were limited.
3-6 became 6-9 when first a scrum penalty - an area Garces adjudged Quins to be in the ascendancy early on - saw Evans knock over three before O'Gara replied after O'Connell's break saw a Harlequin fail to release in contact. That was ultimately the half-time score.
Munster emerged following the turnaround in scintillating form and bettered Quins in all facets, particularly their intensity, as they set off on a purple patch that saw O'Gara knock over three successive penalty attempts to make it 18-9 as the hour mark approached.
Evans did cut the gap to just one score when he landed a penalty on 65 minutes, which set up a grandstand finish, but Munster's determination to silence their recent critics shone through as they held on. O'Connell's emotional words at full-time showed what it meant.
Pen: Evans 4
Pen: O'Gara 6
Harlequins: 15 Mike Brown, 14 Tom Williams, 13 George Lowe, 12 Tom Casson, 11 Ugo Monye, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw (c), 6 Maurie Fa'asavalu, 5 George Robson, 4 Olly Kohn, 3 James Johnston, 2 Rob Buchanan, 1 Joe Marler.
Replacements: 16 Joe Gray, 17 Mark Lambert, 18 Will Collier, 19 Charlie Matthews, 20 Tom Guest, 21 Karl Dickson, 22 Ben Botica, 23 Matt Hopper.
Munster: 15 Felix Jones, 14 Denis Hurley, 13 Casey Laulala, 12 James Downey, 11 Simon Zebo, 10 Ronan O'Gara, 9 Conor Murray, 8 James Coughlan, 7 Tommy O'Donnell, 6 Peter O'Mahony, 5 Paul O'Connell (c), 4 Donnacha Ryan, 3 BJ Botha, 2 Mike Sherry, 1 David Kilcoyne.
Replacements: 16 Damien Varley, 17 Wian du Preez, 18 Stephen Archer, 19 Donncha O'Callaghan, 20 Paddy Butler, 21 Cathal Sheridan, 22 Ian Keatley, 23 Ivan Dineen.
Referee: Jerome Garces (France)
Assistant referees: Neil Paterson (Scotland), Laurent Cardona (France)