Question: What's the difference between playing a guy like Steve Johnson and playing Rafael Nadal Kevin Anderson-- "A guy like Nadal has proven himself over and over again. Mentally, he's so strong. He's created that aura when he steps out there and every match he plays, he plays at a high level. I think it's just experience thing. From a physical side of the game, he is so fit and strong, you've got to match that physicality."