Competing hard against someone and liking them aren’t opposites.

Going at somebody properly is closer to respect than to hostility. Playing down to a person says you did not rate them, and most competitors would rather be taken seriously and beaten. The two things sit together easily once you separate the contest from the opinion. It is why opponents often get on better than teammates do.

Try going as hard as you can against a friend and then being entirely normal afterwards. No gloating and no apologizing for winning either. If somebody cannot manage that, the problem is theirs, and you do not need to play worse to accommodate it.