Florida will play Game 1 winner Alabama on Thursday afternoon while Mississippi State takes on Arkansas in an elimination game Thursday morning.
A solo homer and a two-run triple by Nick Vickerson helped Mississippi State build a 5-2 lead entering the bottom of the seventh.
Florida (42-15) then loaded the bases on a hit batter, a walk and a single prior to Johnson's home run.
Steven Rodriguez (3-1) picked up the win. Austin Maddox pitched a scoreless ninth for the save.
Vickerson and C.T. Bradford each had two hits for the Bulldogs (34-22) but the rest of the MSU lineup was a combined 3-for-25.
Click here for Brad Locke's Inside Mississippi State Sports blog.
Read more in Thursday's NEMS Daily Journal newspaper.