Federer realized in the first 2 games he would need to dip his level to around 20% to keep the match competitive and entertain the fans (remember he is the fan's favorite, even over homeboy).
You could see from the look on his face that he was pretty disgusted with having to make himself look so bad just to keep David in the match. But he really likes the effort David gives and his sportsmanship, so what else could he do?
He had about a 30% first service percentage in the first set, which is about as badly as he can serve without there being an immediate on court drug test, to let David get back in the match from 3-0 up. But even that wasn't enough. He had to also send his groundstrokes into the net time after time, like he did at the Australian Open and Roland Garros to carry out his Wimbledon/Olympic plan (Let Nole and Rafa beat each other up for a few hours).
Federer knew that his fans on MTF would be going nuts, wondering if he had been drugged or didn't get any sleep the night before, and that his haters would say he is finished, pathetic and should retire. But being the sportsman he is, he absorbed all of that. He knew he just had to raise his level slightly, almost imperceptibly, press Ferrer just a bit, and he would take the set, and that is just what he did breaking Ferrer at 4-5 for the first set.
In the second set, Federer gradually and gently raised his level, so he could take Ferrer up with him, and the quality of the match improved. Near the end, Ferrer was playing near his best, and then they made it to the tiebreaker. Federer finally said to himself, enough is enough, and started launching first serve after first serve in. Poor David didn't stand a chance, but at least he felt like he gave Federer a good match, and that's all Roger wanted, as David is too nice a guy.
There was a good friendly handshake between the two near the end. And Roger gave umpire Fedyani two cookies and a wink for his extra effort when they shook hands. I bet most of you missed that exchange...