O'Shea should have got a yellow, which he did, as the rule states that a red should only be shown if the offender is denying a "clear goal scoring opportunity".
There is no mention of "last man" in th erules.
As for Liverpool being the better team "for large protions of it".
If you really believe that, I think you should watch the game again.
United gave The Skause a lesson in football.