The all-premiere competition is a first for the festival, which traditionally kicks off the fall moviegoing season with a dose of European glamour ahead of Toronto later in September.
This year, there has been controversy over a new international festival being started in Rome just two months after Venice that has threatened to eclipse the lagoon city's prestige.
"The best response," festival director Marco Mueller told an opening news conference, "is to watch the films in the competition. Last year, there was a lot of discussion about the film selection — and then came the Golden Globes and Oscars."
Films shown at Venice last year received 23 Oscar nominations.
Catherine Deneuve, who made her first appearance in Venice in 1967 for Golden Lion winner "Belle du Jour," is heading the jury that will award the top prize on the festival's closing day, Sept. 9.
"Venice is a special festival, both for its location and for being international. It has had its high seasons and low seasons, but today it is experiencing a very high season. I think that the festival is at the vanguard for European festivals," Deneuve told a news conference.
One of the first stars to arrive at Venice this year was Scarlett Johansson, who said she modeled her role in "The Black Dahlia" on "a glamorous sort of housewife."
Also in town on the festival's opening day were her co-stars Mia Kirshner, Josh Hartnett and Aaron Eckhart, as well as director Cameron Crowe, who's sitting on the jury, and director Oliver Stone, in town to present "World Trade Center," which is being screened out of competition.
Four U.S. films were competing for the Golden Lion: Besides "The Black Dahlia," the contenders from Hollywood are "The Fountain," starring Hugh Jackman as an immortal seeker, "Hollywoodland," a film exploring the mysterious death of the star of TV's "Adventures of Superman," and "Bobby," Emilio Estevez's look at the last day of Robert Kennedy's life.
The festival also features many films outside of competition, notably this year Stone's drama about the Sept. 11 terror attacks and Spike Lee's "When the Levees Broke. A Requiem in Four Acts," a four-hour HBO documentary.
David Lynch, who will present his new movie, "Inland Empire," will receive the Golden Lion for Lifetime Achievement.