Karlovic v. Mamiit is a rematch of the Bronx challenger semifinal. I was at that match.
Karlovic won in straight sets, going to a tie-breaker both times. Neither player could break the other one's serve.
In the case of Karlovic, his serve is, as is well known, dominating. He can win matches on the serve alone. In the case of Mamiit, his serve is so-so, but Karlovic couldn't break it beacause Karlovic's game, other than his serve, was pretty lousy that day.
Now that Ivo is making the main draw of ATP events, he is going to have to up his game. In this day and age of 120 mph serves, a good serve can win you several matches. But he really needs a more complete game if he's to succeed at the higher levels of tennis.