As the song says, "The old grey mare ain't what she used to be." He's only lost a tiny bit but the effect is quite significant.
Over the past few years, yes. But not this time. I thought Federer was playing his best tennis since 2007 going into the semis and he started off in incredible form.
It's just the match up, and the way he feels pressure and frustration against Nadal. It's just like with Marquez & Pacquiao in boxing. As soon as it starts tightening up, and he hears Nadal's footsteps, he starts having difficulties.
In the past, many of Federer's losses to nadal simply came down to a dozen wasted break points in which he inexplicably dumped a bunch of Raffa's girly 2nd serves into the net. This was not the big problem in the most recent match. But there's always something.
One perplexing issue that still happens to Federer despite countless experiences of getting burned: taking for granted that a point is over. After all these years, you simply MUST assume Nadal will not only run down a ball but make a shot off it as well. Especially the running forehand into the open court - it's almost safe to anticipate that shot and break for it in advance.
One thing about Nadal is tha he never takes a point for granted - he always plays as if he expects his opponent to run down everything he would, no matter how unlikely that is, almost as if he looks forward to having to continuing to play the point. One would think opponents would have learned by now that they too assume this when playing Nadal.