Both Sterling and Alli are being played on the basis of what they might do which works in league football but dodgy on knockouts.
It's not as though we don't have suitable replacements, we do have them.
As for Alli playing out of position, well where's the sense in that? Sometimes you have to do it when other players are injured but that's not the case here.
Dele Alli seems to be a manager's favourite playing in a mates team.