His short backswing (especially off the backhand wing) allows him to execute his chess moves.
I was actually impressed by how he was thinking on court today. For example, players now know that Nadal doesn't like flat balls to his forehand but it was interesting to watch Nalby realize (maybe his coach did) that Nadal does not like deep topspun shots to his backhand and execute that perfectly today. There were so many times today when Nadal sent a ball DTL to Nalby's forehand (hoping for a weak return) only to find that he has to deal with a deep topspun shot to his backhand resulting in a mid court reply.
Two things surprised federer when he played nalbandian
nalbandian has been hitting his fh with some real weight. You can just see the ball kick off the surface and give opposing players fits.
Although nalbandian has been on-fire and playing well, i honestly do not find his game high risk. He looked so comfortable pulling nadal side - side. He was playing his normal game and choosing his spots to change the pace and depth of his shots.
nalbandian would hit the slow junk ball to nadal's bh and then boom the medium fast flat ball would push nadal back deep - take control of the point. Even when nadal made some amazing gets, david just didn't panic because he knew he could always take the upper hand. David is the best at redirecting the ball when he is in trouble. Nadal has nowhere to go on a fast surface against nalbandian.
nadal has always been vulnerable to angles which is why david can master nadal. Nadal doesn't have as much trouble with depth because he stands in the parking lot to retrieve shots. roger doesn't have the same mastery of the angles that david has off both the fh and bh.
ive seen david play really well before but he has never been so comfortable on the court. This is no fluke folks.