Nine-days wonder (5,2,3,3)
I believe the answer is:
flash in the pan
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nine-days wonder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for flash in the pan that I've seen before include "First and only success" , "Nine-days wonder" , "Nine days' wonder" , "Brief success - flambe moment?" , "Failure, after initial promise" .)