At the beginning of the fifth set Federer recieved treatment on both is back and his arm, and when you consider how he had breezed through his previous matches, you would not have expected such wear and tear. He was definitley struggling physcially in that final set; his movement was slower than usual. Safin, on the other hand, looked like he could carry on a lot longer, and maintained a superb level of play.
I've always felt that Federer did not look as physically strong as some of the other players ont he tour and maybe he felt that the was he has been dominating the game, he did not need to be. But today I felt that it really cost him because if you are stronger you will not get those kind of injuries that occur in long matches. In fact, I have heard in the past that most of the fitness work Federer does is related to flexibiltity, eg. work with the medcine ball.
The other thing to consider is that, if you discount the QF Agassi match at the US Open which was played over two days due to rain, Federer had not played a five set match in a grand slam since the 2003 AO against Nalbandian. I think this showed today because he did not have anything left in the tank in the fifth set. Although serving second in that final set did put him under huge amounts of pressure to keep up with Safin, and that contributed to mental cracking. However, Safin had been unlucky in the sense that he was serving second in the previous four sets.
I don't want to take anything away from Safin though, he battled extremently hard despire letting all those match points go. I must also apologise to him because I did not think he stood much of a chance prior to the match. The match was not quite the high quality encounter expected though - the play from both men was littered with unforced errors. But what the match did have was a lot of drama, the point where Safin saved that match point in the 4th set breaker was incredible. At that moment, I thought Federer had won for sure.