Jessica Simpson -- Return of the Jinx?

If Dallas Cowboys fans are looking for a scapegoat ... we might know where to find one...

Just hours before Tony Romo's squad lost in a last second heartbreaker to the NY Giants in Dallas last night ... the 'Boys' most famous bad luck charm decided to publicly weigh in on the match-up.

Here's the message Jessica Simpson left on her Twitter page: "First home game of the season in the new stadium...GO COWBOYS!!!!!!!!"