One secretes nuts and bagels to sustain managing director (US) (9,5)

'us' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'one secretes nuts and bagels to sustain managing director' is the wordplay.
I cannot really understand how this works, but
'one' could be 'ace' ('ace' can be a synonym of 'one') and 'ace' is found within the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
'director' could be 'd' and 'd' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?