Nothing writer observed surpassed description of sports car? (10)

I believe the answer is:

opentopped

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'surpassed description of sports car?' is the definition.
The definition suggests a past participle verb which matches the answer.

'nothing writer observed' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'writer' becomes 'pen' (something which writes).
'observed' becomes 'topped' (I can't explain this - if you can you should give a lot more credence to this answer).
'o'+'pen'+'topped'='OPENTOPPED'

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I've seen this clue in The Irish Times.

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