Drink after drink (6)

I believe the answer is:

chaser

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'drink after drink' is the definition.
(I've seen this before)

'drink after drink' is the wordplay.
'drink' becomes 'cha' (I've seen this before).
'after' says to put letters next to each other.
'drink' becomes 'ser' (I can't explain this - if you can you should give a lot more credence to this answer).
'cha'+'ser'='CHASER'

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(Other definitions for chaser that I've seen before include "Different kind of drink - horse" , "Racing horse" , "second drink" , "Follow-up drink" , "Racehorse - search (anag)" .)

I've seen this clue in the New York Times.

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