Originally Posted by christep

In principle, yes, I would expect the miles upgrade to happen first. But remember that at that point if the flight is seriously over-booked some Diamonds etc. may already have received op-ups earlier in the process. I have sometimes had them confirmed when I did an online check-in over 40 hours before the flight. I have never been "un-op-up-ed", although I guess it may happen on occasion... I would be a bit upset if that happened to accommodate a last-minute mileage upgrade request, but I could have no complaints if a full fare paying passenger turned up at the last minute and they needed the seat.