Deliberately pours open blend (2,7)
I believe the answer is:
on purpose
'deliberately' is the definition.
(synonyms)
'pours open blend' is the wordplay.
'blend' indicates an anagram (I've seen 'blending' mean this (letters blended or mixed into a new form)).
'pours'+'open'='poursopen'
'poursopen' is an anagram of 'ON PURPOSE'.
(Other definitions for on purpose that I've seen before include "Pours open - quite deliberately (2,7)" , "Deliberately, with firm intent (2.7)" , "Deliberately, with full intent" , "Oppose run with deliberate intention" , "Deliberately, intentionally" .)