Mastery means promotion for workman? (9)

I believe the answer is:

upperhand

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'mastery' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'means promotion for workman?' is the wordplay.
'means promotion' becomes 'upper' (I am not sure about this - if you are sure you should believe this answer much more).
'for' means one lot of letters go next to another.
'workman?' becomes 'hand' (hand is a kind of workman).
'upper'+'hand'='UPPERHAND'

Can you help me to learn more?

I've seen this clue in The Irish News.

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