The Spanish director, who heads a jury that includes Hollywood stars Will Smith and Jessica Chastain, took a tough line with Netflix, telling reporters that it would be "an enormous paradox if the Palme d'Or went to a film that can not be seen in cinemas".
Even the Cannes jury president, director Pedro Almodovar, had to succumb to the Will Smith show, admitting he'd always wanted to work with the movie star.
Online giant Netflix has caused a furor in Cannes for refusing to commit to a traditional theatrical release in France of the two films prior to online distribution. Almodovar, reading from a lengthy pre-written statement in Spanish, spoke about the tensions that have grown in a film industry that is trying to grapple with new players like Netflix that don't necessarily premiere movies in theaters.
Netflix allows Smith's children to "watch films they otherwise wouldn't have seen".
According to the Yonhap news agency, Netflix's Chief Content Officer, Ted Sarandos, told reporters the company is "very proud to partner" with distributor Next Entertainment World "to also give Korean viewers an opportunity to see the film in theaters at the same time".
Calling it "the debate of this year", Almodovar was clearly referring to the two Netflix films among the 19 competing for the Palme: Bong Joon-ho's sci-fi fantasy Okja, starring Tilda Swinton and Jake Gyllenhaal; and Noah Baumbach's The Meyerowitz Stories, a dysfunctional-family drama starring Dustin Hoffman, Emma Thompson, Adam Sandler and Ben Stiller. "They said that movies would become obsolete after TV came out, but they still co-exist", he said.
"It would be an enormous paradox if the Palme d'Or went to a film that can not be seen in cinemas", he said in the jury's first press conference.More news: Tayside GP practices affected by NHS cyber-attack running as normal
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"So they have to find a French exhibitor willing to do a day-and-date vanity release or bow out of future Competition involvement?" asked Charlie Lyne, the director of the documentaries Being Clueless and Fear Itself.
Smith, who has not had a film play at Cannes before, was dressed dapperly and posing cheerfully with festival-goers screaming "Will!"
Looking dashing in black tux, Smith joked about his hometown to a group of festival goers, saying, "West Philadelphia is a long way from Cannes".
Stars are arriving under tighter security than in previous years, 10 months after the truck attack in nearby Nice killed 86 people. Festival organizers have said everything was being done to maintain safety and the event's celebratory atmosphere. The packed press screening was met with a tight-lipped, icy silence, which carried over to its tepid press conference held shortly after. When announcing this year's lineup, festival director Thierry Fremaux acknowledged Netflix presents "a unique and unheard of situation for us".
Marion Cotillard and Charlotte Gainsbourg star with Mathieu Amalric - the villain in the 2008 James Bond movie "Quantum of Solace" - in "Ismael's Ghosts", about a filmmaker whose wife disappeared 20 years ago.
In the Cannes version, a new envelope was brought out and the interaction dissolved into a dance that ended with a kiss from Bellucci.
It's the first time any Netflix movies have been considered for the prestigious Palme d'Or award - and it will be the last.