Munster struggled to see off Harlequins before going through to the Heineken Cup knock-out stages.
HEINEKEN CUP Pool 4
Munster (12) 18:
Tries: Horgan, Leamy
Harlequins: (10) 10:
First-half tries by Anthony Horgan and Denis Leamy plus two penalties and a conversion by fly-half Paul Burke made sure Munster topped Pool four.
Quins were never out of the game at Twickenham, particularly with Ugo Monye's breakaway try before half-time.
But the Munster pack were always in charge with Quins' only other points coming from the boot of Andy Dunne.
After Dunne had opened the scoring with an early penalty, Munster forged ahead when good inter-play resulted in Alan Quinlan flipping a pass for Horgan to go over.
Munster should have stretched their lead in the 27th minute when they mauled and rucked their way into a scoring position.
But with a three-man overlap a long, tentative lobbed pass by Leamy found Monye lurking in midfield and he sprinted 80m to go in under the Munster posts.
But following that and right up until half-time it was all Munster as they camped on the Quins line.
The key moment came when Quins hooker Ace Tiatia was sin-binned for coming in at the side of a ruck on his own line.
Munster immediately extracted full retribution when Leamy picked up from the base of another ruck and darted around the fringe to score in the corner to give his side a 12-10 lead.
A 14-man Quins came out fighting in the second half with Gavin Duffy showing up well against his fellow Irishmen.
Munster did stretch their lead in the 50th minute with Burke knocking over a straightforward penalty after Quins were again punished at a ruck.
Burke allayed some of Munster's fears with his second penalty in the 66th minute which put two scores between the sides.
Monye almost broke away again in the 75th minute but he was well tackled by former All Black star Christian Cullen and the danger was averted.
Munster held on, but failing to register a bonus point could see them on the road at the quarter-final stages depending on the rest of the weekend's programme.
Harlequins boss Mark Evans believes Munster will struggle to make an impact in the knockout stages.
"I'm a huge Munster fan but I don't think they can win it this year," said Evans.
"They're a very good side and their record in Europe speaks for itself but I just don't think they've got enough gas in the back five to win the European Cup."
Harlequins: Duffy, Keogh, James, Deane, Monye, Dunne, So'oialo,Jones, Tiatia, Dawson, Rudzki, Miall, Easter, Sherriff, Diprose.
Replacements: Dott, Muggridge, Winters, Molitika, Reay, Staunton, Williams.
Munster: Cullen, Payne, Mullins, Henderson, Horgan, Burke,Stringer, Horan, F. Sheahan, J. Hayes, O'Callaghan, O'Connell,Quinlan, Leamy, Foley.
Replacements: Flannery, McIlwham, Hogan, Williams, Prendergast, Holland, Lawlor.
Referee: J Jutge (France).