As strange a loss as it was to Simon, I still think Federer might just raise his game enough to come through against Murray. It won't be easy, it'll probably be very close but could end up being the match of the tournament - that is if these two don't get to the final and stage it all over again!
1) Murray (against Roddick) looked more comfortable than Federer (against Simon) if you compare them on the basis of the sets they won. But he went for a mental-walkabout in the set he lost 6-1. You can recover from such a lapse against Roddick but against Federer it might set a more ominous tone to the match.
2) Federer has got to be fired up after losing to Murray in Madrid. And the added threat of not making the semis may lend him that extra edge.
3) Both players may be slightly off, what with Federer not practicing as much due to his back, and Murray coping both with the expectation of his Masters Cup Debut and not playing quite the cloud-nine tennis of of recent months. History tells us that experience usually prevails at times like this.
4) ... ok there is no 4, I just want Federer to beat Murray in the Round-Robins so they both make it to the semis!