Crossword Genius

He mastered it as a work out, but I’m much further advanced (1,2,7,5)

Ross

I believe the answer is:

i am streets ahead

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'i'm much further advanced' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'he mastered it as a work out' is the wordplay.
'work out' indicates anagramming the letters.
'he'+'mastered'+'it'+'as'+'a'='hemastereditasa'
'hemastereditasa' with letters rearranged gives 'I AM STREETS AHEAD'.

'but' acts as a link.

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I've seen this clue in the Sydney Morning Herald.
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