Today Djokovic had 60% success on first serve and 61% on second.
So Federer was not doing too well when he got a look at a second serve. Fed also had a poor conversion rate on break points -- 4 of 25. That's 16%, compared to the 40% he won on receiving points overall. (Djokovic converted 4 of 13 break points, or 31%, compared to 33% he won overall.) So I wonder how many of those break points that Federer lost went to second serve.
It would also be an interesting stat from Djokovic's viewpoint, just to see how often he made his first serve when down break point. He made 67% of his first serves overall.