Christian Warner, who started at out-half, landed three penalties to leave Leinster 9-0 in front after 20 minutes, but Leinster were reduced to 14 when flanker Shane Jennings was sinbinned. London Irish failed to capitalise on their mumerical advantage until just before the the interval. Barry Everitt made a clever break before providing the scoring pass to second-row and skipper Ryan Strudwick. Everitt's conversion hit the crossbar, leaving Leinster 9-5 ahead at half-time.
Andy Dunne took over at out-half for the second half with Warner switched to the centre and a long range Dunne penalty put Leinster 12-5 clear.
Eventually, London Irish found some kind of rhythm, after Leinster were again reduced to 14, this time Aidan McCullen yellow carded for a high tackle.
Replacement Mike Worsley, went over for an unconverted try and they moved into 17-12 lead when centre Geoff Appleford's try was converted by Everitt.
Substitute James Cockle added another London Irish try eight minutes from time, and Mark Mapletoft, another substitute, kicked the conversion to leave London Irish 24-12 clear.
With two minutes remaining John McWeeney scored a deserved try, Dunne's excellent conversion from the touchline probably left London Irish nervously looking at the clock but in the end happy perhaps that Leinster are not in their Pool in the upcoming Heineken Cup.
Leinster. P McKenna (M Leek 61); S Keogh, A Magro (K Lewis 21), D Quinlan (A Dunne 40), J McWeeney (F Baynes 78); C Warner, B Willis (S Whelan 70); J Lyne, P Smyth (Capt) (G Hickie 60), P Coyle (N Treston 32), B Gissing (G Quinn 70), A Kearney, A McCullen, D Dillon, S Jennings (L Toland).
London Irish. M Horak; P Sackey, G Appleford, R Hoadley (M Mapletoft 60), P Rossouw; B Everitt, D Edwards (H Martens 32); N Hatley (M Worsley 32),N Drotske (r Kirke 40), S Halford (R Hardwick 32), R Strudwick (Capt), J Fahrensohn, P Gustard (J Cockle 40), C Sheasby, D Danaher.
Referee - S McDowell (Ulster).