Enjoyed this from commenter 'spearmusic':
saw this last night on t.v. wonderful to hear (& see) it (again) just on guitar (with understated keyboard accompany by Bobby Emmons) by the guy who co-wrote the song, Dan Penn. for guitar players & other musicians or non-musicians, one tab i saw had the chords in the verse as G to D to Em, which is incorrect. rather, it's G to F#m to Em, seen clearly on this video; the G to F#m in the key of G gives the song its unique feel IMHO. i like the understated half step modulation (via passing chord D# or D#7) to the key of G# in this live version. (according to Wiki... Dan & Chips Moman co-wrote this song in 1966 during a poker game break in Memphis, with the goal of writing an ultimate cheatin' song. mission accomplished).
Spearmusic is right -- a common progression for this would have been G to D / F# (i.e. D major with F# in the bass) to Em but this song is different! Great performance Bobby and Dan!