Capable of leading the Open -- initially! (2,2)
I believe the answer is:
up to
'capable of' is the definition.
(I've seen this before)
'leading the open initially' is the wordplay.
'leading' becomes 'up' ('up' can be similar in meaning to 'leading').
'initially' suggests taking the first letters.
The initial letters of 'the open' is 'to'.
'up'+'to'='UP TO'
(Other definitions for up to that I've seen before include "Engaged in doing" , "As far as a certain point" , "As far as or as many as" , "As many as, though no more" , "Plotting" .)