Bowl brilliant opener when batting (5)
I believe the answer is:
basin
'bowl' is the definition.
(I know that bowl can be written as basin)
'brilliant opener when batting' is the wordplay.
'opener' says to take the initial letters.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'batting' becomes 'in' (as in batting or being 'in' in cricket).
The initial letter of 'brilliant' is 'b'.
'b'+'as'+'in'='BASIN'
(Other definitions for basin that I've seen before include "requirement for cleansing" , "Water receptacle" , "Sink for washing" , "Kitchen vessel" , "Washbowl" .)