Duke is first to Haydock course (4)
I believe the answer is:
dish
'course' is the definition.
(I've seen this in other clues)
'duke is first to haydock' is the wordplay.
'duke' becomes 'd' (abbreviation).
'first to' suggests taking the first letters.
The first letter of 'haydock' is 'h'.
'd'+'is'+'h'='DISH'
(Other definitions for dish that I've seen before include "Receptacle" , "someone very attractive" , "Directional antenna -- good-looking woman or man" , "Menu item - plate" , "Plate and what's served on it" .)