Course record so modest at the outset (5)
I believe the answer is:
epsom
'course' is the definition.
(I've seen this before)
'record so modest at the outset' is the wordplay.
'record' becomes 'ep'.
'at the outset' indicates taking the first letters.
The initial letter of 'modest' is 'm'.
'ep'+'so'+'m'='EPSOM'
(Other definitions for epsom that I've seen before include "Classic racecourse" , "Mares would triumph here" , "The Oaks and Derby are run here" , "English town, of course?" , "Derby racecourse - salts" .)