10:45 AM PT -- The attorney for the Duffer Brothers tells TMZ, "Mr. Kessler's claim is completely meritless. He had no connection to the creation or development of 'Stranger Things.' The Duffer Brothers have neither seen Mr. Kessler's short nor discussed any project with him. This is just an attempt to profit from other people's creativity and hard work."

A "Stranger Things" casting call looks like a smoking gun in the lawsuit accusing show creators, the Duffer brothers, of ripping off a short film -- because it's black and white proof they jacked the film's title.

We've obtained the casting call, from Aug. 2015, for the role of "Barbara." It includes the following, "You have a self tape request for the Netflix series 'Montauk' starring Winona Ryder." The references to Barb (the description's hilarious and dead-on) and Winona make it clear this was "Stranger Things."

The document also lists Matt and Ross Duffer as writers and directors of the series. TMZ broke the story, the bros were sued by Charlie Kessler, who says he not only made a short film about top secret government experiments entitled "Montauk" ... but he pitched the Duffers a project based on his film.

The timing of the casting call is also super suspect. Kessler says his pitch meeting with the Duffers went down in April 2014. They did NOT strike a deal, but lo and behold, in August 2015 the Duffers were casting for their series, "Montauk."

Netflix had even proudly announced in April 2015 they were buying the series WITH that title.

So, neither the Duffers nor Netflix was bashful about copying Kessler's title ... at the very least. Whether they copied his script could fall to a jury, with the casting call being exhibit A.