As a result of love song's opening (3,2)
I believe the answer is:
due to
'as a result of' is the definition.
('due to' can mean 'because of' or 'as a result of')
'love song's opening' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'song's' becomes 'duet' (I can't explain this - if you can you should believe this answer much more).
'opening' is a charade indicator (letters next to each other) (some letters appear before or \'open\' others).
'o' after 'duet' is 'DUE TO'.
Can you help me to learn more?
(Another definition for due to that I've seen is " Caused by".)