Defeats furrows, absorbing oil, initially (5)
I believe the answer is:
routs
'defeats' is the definition.
(rout is a kind of defeat)
'furrows absorbing oil initially' is the wordplay.
'furrows' becomes 'ruts' ('rut' can be a synonym of 'furrow').
'absorbing' indicates putting letters inside.
'initially' says to take the initial letters.
The initial letter of 'oil' is 'o'.
'ruts' enclosing 'o' is 'ROUTS'.
(Other definitions for routs that I've seen before include "Thoroughly defeats" , "Trounces" , "Utterly defeats" , "old parties" , "Decisively defeats" .)