Not all competitors are opponents, so I don't think it's a good translation.
If you are taking part in a competition, you are a competitor. If you compete against someone else, they are your opponent (and you are theirs). The point is that opponent must always be relative to whoever they are against.
For example, say there is a competition with separate categories, like the men's division and the women's division. A man and woman talking together at the event would agree that they are both competitors, but they are not opponents.
Just to chime in about competitor/opponent. It has to be someone that is somehow "against" or in opposition to you since permutations of words containing gegen imply against: E.g., All the runners in a relay race are competitors, but some are teammates (Mitglieder) while others are opponents.
Could this also be used in a context to point out that he more figuratively knows the strong opponent, as in where the sentence would imply that he has fought strong opponents before and is thus familiar with them? If not, how would you word a sentence like that to create that meaning?