Crossword Genius

Champion runs out of speed (3)

Ross

I believe the answer is:

ace

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'champion' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

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(Other definitions for ace that I've seen before include "Adept" , "Top card or champion" , "One in playing-cards" , "Tennis serve that the opponent can't reach" , "Playing card with a single symbol" .)

I've seen this clue in The Times.
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