As I'm left in penultimate part of contest, I could be this (12)
I believe the answer is:
semifinalist
'i could be this' is the definition.
The definition suggests a singular noun which matches the answer.
'as i'm left in penultimate part of contest' is the wordplay.
I cannot really understand how this works, but
'left' could be 'al' (I've seen this in other clues) and 'al' is found within the answer.
'in' is present in the answer.
'part' could be 'fist' (fist is a kind of part) and 'fist' is found within the leftover letters.
'contest' could be 'semi' (semi is a kind of contest) and 'semi' is found in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
(Other definitions for semifinalist that I've seen before include "Contestant among the last four" , "One in last four of a contest" , "One of last four left in competition" , "One of last four in knockout competition" .)