That's how he has been winning his matches all week. By digging deep. His A game isn't working. For me it's nice to see him grinding it out when he can't hit winners. Grinding his way out of this bad form. Unlike Shanghai and Cincy where he was making errors but still playing the right way, here he is digging in and I am loving it.
This could be said about every match this tournament, except for the Medvedev match. Fed didn't play well but he won on experience and variety, and of course was lucky that he didn't have to face a really strong player.