It has divided the critics, who have either praised it for its exuberant, operatic, roaring approach to its material – or derided as a crass, tin-eared rendering of F Scott Fitzgerald's precisely tuned text.
"People are going out to see it" after a "very nervous [opening] weekend" when it was up against "giant action films", he said.
He was used to audience reaction outgunning the critics' voices, he said. "Look, I made Moulin Rouge. And Romeo + Juliet, and Strictly Ballroom for that matter, and they never got those high critics' scores."
He noted that in the last week the novel had sold more copies than in the author's lifetime.
The Australian director described how, a decade ago, he had been travelling across Siberia by train with a "bottle of Australian red and a couple of recorded books". He switched on The Great Gatsby, which he had read as a young boy. It was a revelation. "It was us, where we are now are, this great mirror to reflect back on us," he said.
Craig Pearce, his co-writer, added: "It had a resonance today that was so strong in terms of what it was saying about the financial climate and the global financial crisis, and incredibly Scott Fitzgerald predicted this with a [car] crash, symbolic of a greater crash which had not yet happened but was about to." The 1929 Wall Street Crash came just four years after the novel's publication.
Luhrmann paid tribute to the Fitzgerald scholars, including Professor James West of Penn State University, who had "kept us in check" in adapting a "sacred text".
The film's British co-star, Carey Mulligan, who plays Gatsby's great love, Daisy Buchanan, described how Luhrmann gave her "six books to read" before sending her to Princeton, which holds the Fitzgerald literary archive, to consult scholars.
She immersed herself in the life of Fitzgerald's wife, Zelda, as well as that of Ginevra King, with whom the author had a relationship, drawing deeply on her side of their correspondence (his does not survive).
"The language, how she uses words – it was completely how Daisy talks and writes," said Mulligan.
Leonardo DiCaprio, who stars as the tortured Gatsby, also described how the writers and cast drew on Fitzgerald's early version of Gatsby, Trimalchio . "Ultimately it became the tragedy of this man in the new world where everything is possible and he is trying to become a great American, a great Rockefeller, and somewhere along the way he has lost the sense of who he is and is trying to hold on to the mirage that is Daisy Buchanan," he said.
Nineteen films compete for the Palme D'Or this year. None of them is British, though there is great anticipation about The Selfish Giant, Clio Barnard's second feature, which premieres in the Directors' Fortnight .
The Coen Brothers' latest is up against work by directors including Asghar Farhadi, who won an Oscar for A Separation; and Nicolas Winding Refn – who is reunited with Drive star Ryan Gosling in Only God Forgives, which also stars Kristin Scott Thomas.
Mulligan is quite the flavour of the festival: she also appears in the Coens' Inside Llewyn Davis, set in the 1960s New York folk scene. Her husband, Marcus Mumford, has also worked on the film's music.
Chairing the unusually starry jury is Steven Spielberg; his colleagues include directors Ang Lee and Lynne Ramsay, and actors Christoph Waltz, Daniel Auteuil and Nicole Kidman. Spielberg said Cannes was a "breath of fresh air" in contrast to that other great cinematic competition – the Oscars.
"It is such a relief that we are seeing movies and caucusing and deliberating and we don't have to go through the campaigning, which follows awards season in America like a political cycle. We had a campaign for the 2012 election and then we had a campaign for the Oscar election," he said.
He had no qualms about picking winners and also-rans. "We're always judging, sitting in personal private judgment of the movies we see anyway... And, also, everyone sits in judgment on us. This is our turn."
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