"main squeeze": query

[Gerald Cohen]

   I was recently surprised to learn that "main squeeze" (one's
boyfriend, girlfriend or spouse) is also attested as "a person having
principal authority; boss." See _HDAS_.

    But what was the original reference to the squeezing going on in
this latter meaning of "main squeeze"? Exactly who or what was being
squeezed by the person in authority?

     BTW, I recently noticed an instance of "main squeeze" in a 1913
baseball context (_San Francisco Bulletin_ May 21, 1913, p.16, col.
7; title: 'Surprising Number of Coasters Making Good in East': 'Let's
go down the list and look the grads over and see what they are doing
back there [in the major leagues]:
     'Agnew gets credit of making the St .Louis Browns what they are.
He is Stovall's main squeeze behind the pan.' --(i.e., behind the
plate).

---Gerald Cohen