Convincing victory (9)
I believe the answer is:
landslide
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">convincing victory</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 landslide that I've seen before include "Overwhelming election win" , "convincing victory" , "Shifting of ground" , "Overwhelming victory in election, or a natural disaster" , "easy victory" .)