Climactic moment from Borg, as McEnroe discovered (6)
I believe the answer is:
orgasm
'climactic moment' is the definition.
'borg as mcenroe discovered' is the wordplay.
'discovered' says the answer is hidden in the clue (remove the letters covering the answer in the clue).
'ORGASM' is hidden within 'borg as mcenroe'.
'from' is the link.
(Other definitions for orgasm that I've seen before include "Immoderate excitement" , "Bout of intense excitement" , "Fit of intense excitement" , "Practising conjugation may achieve it" .)