One's utmost to equalise with the champion (5,4)

I believe the answer is:

level best

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'one's utmost' is the definition.
'level best' can be an answer for 'utmost' (synonyms). I'm unsure of the 'one's' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for level best that I've seen before include "Hardest" , "Maximum efforts" , "joint winners?" , "Utmost effort" .)

I've seen this clue in the Evening Standard.

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