Tighten mangle (5,2)
I believe the answer is:
screw up
'tighten mangle' is the definition.
'screw up' can be an answer for 'tighten' (thesaurus). I'm unsure of the 'mangle' bit.
'tighten mangle' is the wordplay.
'tighten' becomes 'screw' (screwing is a kind of tightening).
'mangle' becomes 'up' (I am not sure about this - if you are sure you should believe this answer much more).
'screw'+'up'='SCREW-UP'
Can you help me to learn more?
(Other definitions for screw up that I've seen before include "put cap on?" , "Mishandle a situation" , "Summon" , "Completely mismanage a situation" , "Completely mismanage (colloq.)" .)