Regularly seen before defeat, last one on the way (2,5)
I believe the answer is:
en route
'on the way' is the definition.
(synonyms)
'regularly seen before defeat last one' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'before' means one lot of letters go next to another.
'defeat' becomes 'rout' (rout is a kind of defeat).
'last' indicates one should take the final letters.
The final letter of 'one' is 'e'.
The alternating letters of 'seen' are 'en'.
'en'+'rout'+'e'='EN ROUTE'
(Other definitions for en route that I've seen before include "While travelling" , "In transit (French)" , "March" , "'On the way (2,5)'" , "As part of a journey" .)