Affect greatly, excited at the finish (5)
I believe the answer is:
upend
'affect greatly' is the definition.
(I've seen this before)
'excited at the finish' is the wordplay.
'excited' becomes 'up'.
'at' means one lot of letters go next to another.
'the finish' becomes 'end' (I've seen this before).
'up'+'end'='UPEND'
(Other definitions for upend that I've seen before include "Tip right over" , "Topple" , "Tip on side" , "Affect greatly" , "Set (something) vertical" .)