Astonishing feat of vehicle moving up in race (7)
I believe the answer is:
miracle
'astonishing feat' is the definition.
(I've seen this before)
'vehicle moving up in race' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'moving up' says the letters should be written backwards (for a down clue).
'in' indicates putting letters inside.
'race' becomes 'mile' (mile can refer to a mile-long race).
'car' reversed gives 'rac'.
'rac' going inside 'mile' is 'MIRACLE'.
'of' acts as a link.
(Other definitions for miracle that I've seen before include "It's said to happen by the divine intervention" , "something amazing" , "Wonder, sign" , "Event that appears to break the law of nature" , "Divine action" .)