The most common and most likely answer to this crossword clue is the 7 letter word MATCHUP
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More clues leading to the result MATCHUP
Buddy explains!

The straight part
We know that "one-to-one competition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one-to-one competition = matchup.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MATCHUP mean?
MATCHUP noun- A pairing of two things, people or teams, especially for a competition