While that was a boost for the club's director of rugby, McGeechan, equally important for him was to see the 15-times capped back row man Rees successfully negotiate his first game for nine weeks.
Rees damaged his medial ligaments against Harlequins at the start of the year and was forced to sit-out England's RBS Six Nations campaign. By playing the full 80 minutes against the Irish he proved he is back on course to resurrect his Test career.
England manager Martin Johnson would have loved to have had a fully fit Rees to pick in his back row this season - and McGeechan and his fellow Lions selectors are bound to want to closely examine his credentials when they pick their back row options for South Africa this summer.
There were 11 points from the boot of Danny Cipriani as the Wasps rocked their London rivals.