Advanced equipment amazes top dog (5)
I believe the answer is:
akita
'dog' is the definition.
(Akita is a breed of dog)
'advanced equipment amazes top' is the wordplay.
'advanced' becomes 'a' (abbreviation).
'equipment' becomes 'kit' (kit is a kind of equipment).
'top' suggests taking the first letters (in a down clue, the first letter is top).
The first letter of 'amazes' is 'a'.
'a'+'kit'+'a'='AKITA'
(Other definitions for akita that I've seen before include "powerful dog" , "dog from Japan" , "heavy brute?" , "Japanese breed of dog" .)