S Scanlon 1 Try
They should have taken the lead when awarded a penalty in the opening minute but Ian Keatley's effort from the 22 in front of the posts was well off the mark.
Then they lost their number 8 and captain Peter O'Mahony in the 10th minute after he shipped a heavy knock in a tackle although he did trot off the field un-aided, 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 chance. Quick recycled ball and a long floated pass had Doug Howlett scooting for the corner only to be bundled into touch at the corner flag.
Irish won the ensuing lineout broke downfield to lay siege to the Munster line, their efforts thwarted by superb Munster defence that resisted a series of drives for the line close to the posts.
Eventually we had the first score of the game, a 35th minute Keatley penalty and remained like that at 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. Highlight of that period was Keatley's deft pass that put Denis Hurley through but Irish scrambled well in defence.
The stalemate continued until the 58th minute when Munster broke left with a mazy Keatley run, Niall Ronan chipped ahead, a ball that had Tom Homer in all sorts of trouble and Sean Scanlon was up quick to gather and score.
Jonathan Joseph's run up the west touchline forced Munster to concede a penalty and Irish opted for a close in lineout drive that once again was resisted by superb Munster defence.
Replacements Peter Borlase and James Sandford got involved in an altercation that saw Borlase get a yellow and Sandford a red card and soon after Niall Ronan - who had a fine game throughout - followed them to the sideline 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.
Damien Varley was the third Munster player to be yellow carded and London Irish had the final say with a try deep in injury.
Munster: S Scanlon (S Deasy 64th min); D Howlett, D Barnes (S Zebo 55th min), L Mafi, D Hurley; I Keatley, D Williams (P Striner ht); M Horan (W du Preez 55th min), M Sherry (D Varley ht), S Archer (P Borlase 64th min); I Nagle (D O'Callaghan (31st min temp & 55th min), M O'Driscoll; B Holland, N Ronan, P O'Mahony (T O'Donnell (10-17th min & 58th min).
London Irish: T Homer; T Ojo, J Joseph, D Bowden, M Yarde; A Jarvis, P Hodgson; M Lahiff, D Paice, F Rautenbach; N Kennedy, M Garvey; K Roche, J Gibson, R Thorpe. Replacements: M George, L Halavatau, B Blaney, J Sandford, T Alexander, A Gray, R Samson, S Shingler, A Thompstone, A Watson.
Referee: Alain Rolland.