This is certainly possible. This is the first match in probably 7 or 8 years where he was a huge underdog. He was an underdog in most of the recent clay matches against Nadal, but all of them were close until RG '08. After that beating, betters had lost all hope that Fed would beat Nadal on clay. The betting line was massively in favor of Nadal, and everyone had all but written off any chance Federer had against Nadal on clay after losing to Nadal on grass and hard courts.
roger mentioned something in one of the articles that struck me...something so basic.
"I just wanted to stay positive".
I think he knows by now playing nadal that anything can happen-getting broken, losing 40-0 leads, blowing bps. so pretty much accept that it MIGHT happen and just play the points as points. So he was still calm even in the final game when he was down 15-40.
one thing i did for sure notice is that the points were unusually short today and nadal couldn't impose his grinding style on federer like usual. He also couldn't hook federer off the court on the big points on fed's bh side like he usually does and i think it has a lot to do with his lack of confidence on the madrid courts - where he been complaining about his rhythm. he just couldnt find his usual depth and federer executed quite a few one-two serve fh punches.
i also liked how federer took a little off his serve in the deuce court and was content to slide it out wide and control the points with his fh rather than go for the ace every time. when nadal has time he can hit a mean bh return in the deuce court off 2nd serves, but when you hit off pace 1st serves with slice he cant get it back in the court with interest and federer can impose his fh.
not too much new strategy from federer but he did use the bh drop shot to perfection today. this match reminds me of the mc 07 final in a few ways except the result was the opposite.