One setting the tempo in space race (5)
I believe the answer is:
pacer
'one setting the tempo' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'in space race' is the wordplay.
'in' says the answer is hidden in the clue.
'PACER' is hidden in the letters of 'space race'.
Can you help me to learn more?
(Other definitions for pacer that I've seen before include "One walking steadily" , "early race leader?" , "Racehorse" , "Racing horse with an unusual gait" , "Competitor" .)