Substitute comes in last and interrupts (5-2)
I believe the answer is:
stand in
'substitute' is the definition.
(I know that substitute can be written as stand-in)
'in last and interrupts' is the wordplay.
'in' indicates the answer is hidden within the clue.
'STAND-IN' is hidden in the letters of 'last and interrupts'.
'comes' is the link.
(Other definitions for stand in that I've seen before include "Substitute's" , "Vocal pieces" , "Deputise; sail close to the shore" , "Sub" , "Representative" .)