A coach called me and told me his observations at this last US Open. He said he sat in the lowest row, just behind Federer. He noticed a huge amount of sidespin, as well as topspin, mainly on his forehand.

He also noticed how much he hits across the ball with his racquet, rather than following the ball's path.

I like to remind you that most coaches still counsel you to follow the path of the ball, as if you were hitting "five balls in a row."

This is something you can address on your own game. You can still hit down the line or even inside out forehands by lagging the racquet head behind your hand, even while hitting across to the left, towards the left side of your body (for a right handed forehand). The ball will go wherever the racquet is facing.

Lift as well, with the racquet in a windshield wiper motion, as if you had a large glass window in front, sweeping it, but without breaking it.

The tendency, for a human being playing tennis, is hitting forward. Using this glass window analogy will give you still a strong shot, but it will make it safe, penetrating, and allow you to hit harder and harder every day. The mistakes will be fewer and fewer, no matter how hard you hit.