The fact that London Irish scored their sole try deep in injury-time highlights the merit of this Munster success, which owed much to the perfomance of their pack and the team's defensive prowess.
The province should have taken the lead when awarded a penalty in the opening minute but Ian Keatley's effort from the 22-metre line, in front of the posts, missed the target.
Then they lost their number 8 and stand-in captain Peter O'Mahony in the 10th minute after he shipped a heavy knock in a tackle although he did trot off the field unaided. He was replaced by Tommy O'Donnell but returned before the quarter had ended.
It was O'Mahony's incursion into the Irish 22 that presented Munster with their best early chance. Quick recycled ball and a long floated pass had Doug Howlett dashing towards the corner, only to be bundled into touch at the corner flag.
Irish won the ensuing lineout and broke downfield to lay siege to the Munster try-line. Their efforts were thwarted by superb Munster defence that resisted a series of drives for the line close to the posts.
Eventually, Tony McGahan's men secured the first score of the game. 35 minutes were gone when Keatley knocked over a penalty and 3-0 is how it remained for the break.
Munster opened the livelier in the second half with O'Mahony continuing to impress with ball in hand, as did Stephen Archer and the hard-working Mick O'Driscoll.
The highlight of that period was Keatley's deft pass that put Denis Hurley through but Irish scrambled well in defence and recovered the situation.
The stalemate continued until the 58th minute when Munster broke down the left thanks to a mazy Keatley run. Niall Ronan then chipped ahead and with Tom Homer under all sorts of pressure, the speedy Sean Scanlon was up quick to gather the ball and touch down.
Jonathan Joseph's run along the west touchline forced Munster to concede a penalty and Irish opted for a close-in lineout drive that once again was blocked off by some determined defending from the hosts.
Replacements Peter Borlase and James Sandford got involved in an altercation that saw Borlase get a yellow card and Sandford a red card.
Shortly afterwards, flanker Ronan, who had a fine game throughout, followed them to the touchline as the recipient of a yellow card.
Adrian Jarvis kicked London Irish's first points in the 76th minute but Keatley cancelled out that score moments later, nudging his side into an 11-3 lead.
Replacement hooker Damien Varley was the third Munster player to be sin-binned and London Irish had the final say with a converted try in the dying seconds, as Richard Thorpe picked off the base of a scrum and dived over. Jarvis converted.
MUNSTER: Sean Scanlon; Doug Howlett, Danny Barnes, Lifeimi Mafi, Denis Hurley; Ian Keatley, Duncan Williams; Marcus Horan, Mike Sherry, Stephen Archer, Mick O'Driscoll, Ian Nagle, Billy Holland, Niall Ronan, Peter O'Mahony (capt).
Replacements used: Tommy O'Donnell for O'Mahony (10-17 mins, blood sub), David O'Callaghan for Nagle (31, temp), Peter Stringer for Williams, Damien Varley for Sherry (both half-time), Wian du Preez for Horan, Simon Zebo for Barnes, David O'Callaghan for Nagle (all 55), Tommy O'Donnell for O'Mahony (58), Scott Deasy for Scanlon, Peter Borlase for Archer (both 64).
LONDON IRISH: Tom Homer; Topsy Ojo, Jonathan Joseph, Daniel Bowden (capt), Marland Yarde; Adrian Jarvis, Paul Hodgson; Max Lahiff, David Paice, Faan Rautenbach, Kieran Roche, Matt Garvey, Richard Thorpe, Jamie Gibson, Alex Gray.
Replacements used: Pete Synott for Gibson (half-time), Leo Halavatau for Rautenbach, James Sandford for Synott (both 50), Adam Thompstone for Ojo, Anthony Watson for Yarde, Brian Blaney for Paice (all 71). Not used: Mark George, Tom Alexander, Ross Samson; Steven Shingler.
Referee: Alain Rolland (IRFU)