One thing that I should have mentioned about the floundering Diamondbacks is that Randy Johnson is on pace to win one third of their games. Right now they have 36 wins and Johnson has 12 of them.
No one has won that large a percentage of their team's wins since Steve Carlton and Gaylord Perry both did it in 1972. Before those two, no one had accomplished this "feat" since 1952. Johnson would be the first man to do it since the advent of the five-man rotation (or at least since it became de rigueur). Of course, if he does get traded that puts the kibosh on this dubious mark, but then again, if he does stick with the D-Backs, they don't seem to be doing much when Johnson is not on the mound.
Below are all the pitchers who have done it since 1900. Note that four-man rotations did not become commonplace until the late 1890s, so 379 men did it in the 19th century.