Finished on tee in Open? (5)
I believe the answer is:
overt
'in open?' is the definition.
(I've seen this before)
'finished on tee' is the wordplay.
'finished' becomes 'over' ('over' can be similar in meaning to 'finished').
'on' means one lot of letters go next to another.
'tee' becomes 't'.
'over'+'t'='OVERT'
(Other definitions for overt that I've seen before include "Conspicuous" , "Open and obvious" , "Plainly apparent" , "Openly displayed" , "Open and unconcealed" .)