Important horse race (7)
I believe the answer is:
classic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">important horse race</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for classic that I've seen before include "Important horse race" , "Flat race" , "Of the highest order - the Derby, for example" , "Oaks perhaps" , "Epsom Derby or St Leger Stakes, for example" .)