Joker also opens in earnest overseas timed to its U.S. launch. Tracking suggests it will bow to $60 million or more abroad, a strong start for an R-rated title that is far from a normal Hollywood superhero project (the DC logo doesn't even appear in the credits).

The generally well-reviewed movie cost at least $64 million to produce before marketing. Village Roadshow Pictures, Warners' longtime partner, and Bron Studios each have a stake in the pic, which made the rounds at the fall film festivals in search of awards glory. Phoenix, in particular, has drawn praise for his performance.

No other movie is daring to open nationwide opposite Joker, meaning it will own the weekend.

To date, there have been no credible or specific threats made to theaters, according to the FBI and law enforcement agencies in Los Angeles and New York. Still, police in both those cities say they may deploy officers to various cinemas screening Joker (that's not unusual for a high-profile release, including Star Wars films).

Theaters in other parts of the country are also taking precautions, including the Texas-based Alamo Drafthouse, which said it will have additional security present after receiving inquiries from customers.

In the U.S., Joker will begin its preview run at 4 p.m. Thursday. By Friday morning, it will be playing in more than 4,300 theaters, including on Imax and premium large-format screens.