A cinema worker occupies the red carpet of the Rome Film Festival to protest against the budget cut in the culture funds October 28, 2010.[Photo/Agencies]?

Keira Knightley and Eva Mendes face off as the two rival beauties in "Last Night," the story of a married couple grappling with the temptations of infidelity that kicked off the Rome film festival on Thursday.

The opening ceremony was marred by a protest over the Italian government's drastic cuts to funds for cultural events, with some 800 people storming the red carpet.

Knightley and Mendes did not take to the red carpet and were whisked into the theater alongside the rest of the film's cast, surrounded by bodyguards.

In the film, Knightley leaves behind her trademark costume roles to play Joanna, a young woman living in a posh Manhattan loft who becomes jealous when she meets her husband's sexy new colleague, played by Mendes.

When he and Mendes go on a business trip together, Joanna bumps into her French former lover -- and finds herself confronted with the same dilemmas about cheating as her husband.

The film develops into the parallel tales of how the couple spent their tempting evenings in separate cities, using frequent close-ups to explore the emotional side of the story.

Knightley described "Last Night," Iranian-American screenwriter Massy Tadjedin's directorial debut, as a thought-provoking film that leaves it to the audience to decide just exactly what constitutes cheating.

"I think everyone can recognize the scenarios that happen within this piece, I think that most people have at least been one person, if not all four, at some point in their life," Knightley told reporters after a press screening.

"In most films there are goodies and baddies, what I liked about this script is that it did not take a standpoint, that there is no conclusion," she said.

The film, which also casts "Avatar" star Sam Worthington and French actor Guillaume Canet, opened the fifth edition of the Rome film festival, which runs until November 5.

Also screening on Thursday was "Dog Sweat," a film by Iranian director Hossein Keshavarz following the lives of six young people rebelling against the rigidity of conservative Islamic society in present day Iran.

The film was shot clandestinely throughout Tehran before the disputed presidential election of 2009.