Many internationals such as Paul O'Connell and Donnacha O'Callaghan were not available for Munster tonight and, despite a typically resolute performance, it showed on the pitch.
Despite this, there was cause for optimism in the performances of young players such as Brian Tuohy and Martin McPhail.
London Irish took the lead after a defensive mistake by Anthony Horgan, Kieron Dawson taking advantage of a fortunate bounce to score a try, which Mapletoft duly converted.
With London Irish up by seven at half-time, there was wholesale changes in the Munster line-up.
The errors continued for Munster however, as the substitutions continued throughout the half.
There was some hope after McPhail and Tuohy combined for a try, but Jason Holland failed to convert.
Munster continued to defend well however, before London Irish substitute Pierre Durant got in for another try ten minutes before full time.
C. Cullen, M. Lawler, M. Mullins, J.Holland, A. Horgan, P. Burke, E. Reddan, G. McIlwham, J. Flannery, M. Storey, T. Hogan, T. Hayes, S. Keogh, J. Williams (captain), D. Leamy.
Replacements.J. Storey for Mullins, R. Henderson for Holland, M. Prendergast for Reddan, D. Ryan for Hayes, E. McGovern for McIlwham, J. Blaney for Flannery (all 40), M. McPhail for Lawler (53). McIlwham for Storey, Holland for Burke, B. Tuohy for Horgan (all 60), B. Murphy for Tuohy (71).
M. Horak, J. Bishop, G. Appleford, N. Mordt, P. Sackey, M. Mapletoft, P. Hodgson, N. Hatley, A. Flavin, R. Hardwick, B. Casey, N. Kennedy, P. Poulous, K. Roche, K. Dawson (captain).
Replacements, P. Murphy for Roche (40), P. Durant for Hardwick, D. Paice for Flavin, R. Thorpe for Poulous, K. Barrett for Hodgson, R. Laidlaw for Mapletoft (all 61).