Just based on the observation of the highlights on Youtube, I get the impression Djokovic was much faster than Nadal that night. Nadal relies heavily on mixing it up with his forehand, and for that he needs some really good movement, circling the backhand and getting there early so he can take advantage of all the angles. But Djokovic kept him on the defense a lot, and Nadal was often just barely getting to the ball and chipping it back with slices. Because Nadal wasn't very quick, his plays becomes predictable, and Djokovic can use his speed to take the ball on the rise to keep Nadal on defense.
Nadal was certainly trying to go on the offense, he hit a lot of flat forehands, looking for easy points or damage Djokovic's defense, but Djokovic's court coverage is still good, he doesn't get bothered by aggressive play, especially from someone who doesn't usually do that. Djokovic with his flexibility and speed, always gets to the ball quick and even if sometimes he doesn't, he can use flexibility to place the ball anywhere, which makes him always unpredictable in his play pattern. Basically, Nadal is shoehorned into only a few play patterns that works for him, while Djokovic has many more play patterns that work for him, keeping him in the points. Also, Nadal's serve wasn't hurting him.
But based on what I saw, Nadal will still be the favorite at the French Open. Suffering from speed disadvantage isn't as huge on clay. Inconsistent bounces, windy conditions, Djokovic can't hug the baseline that much on clay. Nadal has been working on his strokes, hitting the ball with a lot of power still. I think it's enough to keep him in dominant positions in rallies on the clay.
