Mother is the one who wins a game of chess (5)
I believe the answer is:
mater
'mother is the one who wins a game of chess' is the definition.
'mater' can be an answer for 'mother' (old-fashioned term for mother). I am unsure of the rest of the definition.
'mother is the one who wins' is the wordplay.
'mother' becomes 'ma' (ma can mean mother).
'is the one who wins' becomes 'ter' (I can't explain this - if you can you should give a lot more credence to this answer).
'ma'+'ter'='MATER'
Can you help me to learn more?
(Other definitions for mater that I've seen before include "mum's the word" , "One marrying" , "Mother (Latin or old slang)" , "Mother (sl.)" , "Dam" .)