Commentators just said that pror to this match, Karlovic had won 49 out of 50 service games. Andy's now broken him 2 out of 4. It is one of his greatest assets that he can get a controlled return on serves that others can bearly get a racket on !
Great variety, sometimes serving and volleying, but generally after the fiest few games any rally he is winning the vast majority of the time, which is to be expected.
I don't think he's had to face that many break point opportunites in recent times. I can't think of a single match, in fact. Grand Slams included. It just highlights how good Andy is at returning the ball and how his game matches up brilliantly against big servers.