Relies on just one of two US actors? (9)
I believe the answer is:
fairbanks
'one of two us actors?' is the definition.
(Douglas Fairbanks or Douglas Fairbanks Jr)
'relies on just' is the wordplay.
'relies' becomes 'banks' (I've seen this before).
'on' says to put letters next to each other.
'just' becomes 'fair' (just can mean fair in the sense of showing justice).
'banks' after 'fair' is 'FAIRBANKS'.
(Other definitions for fairbanks that I've seen before include "Alaskan city" , "actor" , "US city" .)