Today I watched how difficult was for Nadal to win Verdasco. Now in difference from the clay a ball bounces quicker and stronger ,and Nadal doesn't have time to return all unbelievable balls. Just hit the ball harder and the game will change radically. Now great endurance goes to the second plan, and volleying, hard hitting, quick responses, tactics come to the first. Now a ball doesn't stick in the clay, it doesn't slow down, so timings change radically.