Close race overshadows who came last? (5)
I believe the answer is:
loser
'who came last?' is the definition.
'close race overshadows' is the wordplay.
'overshadows' says the answer is hidden in the clue.
'LOSER' can be found hidden inside 'close race'.
(Other definitions for loser that I've seen before include "Defeated competitor" , "Opposite of winner" , "Person who's a failure" , "One vanquished" , "Roles for the defeated" .)