James Pablo tells TMZ he was backstage at Mariah and Lionel Richie's show Thursday night at San Diego State's Viegas Arena to interview their opener. He says he had a press pass that was attached to a lanyard around his neck, and had every right to be there.

James says he saw Mariah backstage, and asked to take a pic with her -- which he says she OK'd. When he tried going in for the selfie, James says her bodyguard allegedly yanked his lanyard -- which was still around his neck -- and dragged him outside.

Once he was out, James tracked down cops and filed a police report ... saying he wanted to press charges. Law enforcement sources confirm a battery report was taken and the investigation is ongoing.

As for Mariah ... sources close to her tell us James was an obsessed fan who snuck backstage with a fake badge. Her bodyguard pulled James away when he saw him grab her dress and feared he was going to attack her.

James insists he had a valid press credential to be backstage, and denies grabbing Mariah's dress.