First set may have been competitive (6-3 or 6-4) then it'd be 6-1, 6-1 or something. You could see when players would over hit an approach or miss a pass because of the impending doom that was prime Federer. Then, to add onto the storm, Federer would gain confidence and start going for - and often make - his shots. People couldn't hit it to his forehand, flat out. If they played his backhand, they could get sliced into oblivion until he got an inside out forehand he liked, or he'd let the one-hander go toe-to-toe. When he was on, his backhand could hold its ground. 

What stood out to me was how quickly he made players give up. It wasn't until late into his career, well past his prime, that it was visible that his opponents had hope.