To find out, I used a data set of all ATP-level matches from 2001 to 2010 and counted, among other things, how many sets ended in a tiebreak.

In that span, about 17 percent of sets ended in tiebreaks.  Indeed, Karlovic has played tiebreaks at a higher rate than anyone else.  And it isn’t even close.

After eliminating everyone who played fewer than 200 sets in the last decade, we’re left with 205 players.  Of those, 33 guys reached a tiebreak in at least 20 percent of sets.  Only 7 played tiebreaks in more than a quarter of sets.  Karlovic reached a tiebreak in 40 percent of sets, more than anyone else in this time period.

Rounding out the top of the list are Chris Guccione at 35% (in only 203 sets), John Isner and Wayne Arthurs at 33%, and Alexander Waske at 31%.