Top five pitching duos

Zack Greinke and Clayton Kershaw form a formidable pitching duo. AP Photo

When the Los Angeles Dodgers signed Zack Greinke this offseason, he gave them -- along with lefty Clayton Kershaw -- one of the top front ends of a rotation in baseball. Together, the duo is arguably the best one-two punch in the game, a pair truly capable of winning four games in a seven-game series.

Are they the best in the game? I decided to pore through some advanced metrics (and sprinkle in a little subjectivity) to determine the top five duos in the game right now.