Smooth start to surprising defeat (5)
I believe the answer is:
slick
'smooth' is the definition.
(slicking is a kind of smoothing)
'start to surprising defeat' is the wordplay.
'start to' says to take the initial letters.
'defeat' becomes 'lick'.
The first letter of 'surprising' is 's'.
's'+'lick'='SLICK'
(Other definitions for slick that I've seen before include "Showing Polish" , "Glibly assured" , "polished performance" , "Sleek - film of oil" , "Bedeck" .)