I went to both the SF and Final in Dallas. Me and one friend in USA stuff. No problems from Mexico fans.
It's the same as being a visiting fan at any sporting event. If you mind your own business and don't make yourself a target by taunting other fans or being generally obnoxious, it's extremely unlikely you'll find any problems, regardless of what you're wearing or whether you cheer your own team's successes. Especially if you can handle a few wayward comments and taunts without losing your mind. Everyone is chill one-on-one. The tiny US supporters section just becomes a target by default, since that's where all the drums, flags, chants, etc are coming from.