Well, after tonight's 5-set victory over Andreev, Federer is actually past the halfway point, but everything still applies!
The last few Grand Slam tournaments, you can sort of see Federer's preparation for the later rounds (especially an anticipated match against Nadal). For example, at the French Open, he was leaving a bigger margin for error around the court, not aiming quite so close to the lines. That was working well, cutting down on unforced errors, but he seemed to forget that strategy in the final.
Now in the US Open, different tactics but same theme. Against Alves, a right-hander, Federer was hitting tons of slice serves breaking wide in the deuce court. Why do that against a right-hander? It may still prompt a weak return that can be volleyed or angled away for a winner. But I think it's really practice for Nadal. The same play came up now and then against Andreev.
Another tactic that proved counterproductive against Andreev was to consistently approach and then volley over to the deuce side, Andreev's forehand, his best shot. Roger lost a number of points to passing shots where clearly the higher percentage play was to go to the backhand. I think he's been focusing so much on Nadal that those attacks, to a left-hander's backhand, are stuck in his head against other opponents.
I was pleased to see Federer hustling around the court and banging flat backhands against Stepanek. That's the style that will intimidate even the toughest opponents. Just have to remember to keep doing it in the last couple of rounds. I hope Muller in the quarterfinals will be an easier match, the better to recover from 5 sets in the round of 16.