A low-budget horror movie is set to win the box office this weekend, while a much-hyped follow-up to "The Social Network" is struggling.

"Other Mommy," from Universal and Blumhouse's Atomic Monster, made $3.6 million from Thursday previews, The Hollywood Reporter said. It opened in about 3,200 North American theaters, and Universal was projecting a $20 million weekend. Jessica Chastain stars in a dual role, as a mother and a sinister double who targets her 8-year-old daughter. Rob Savage directed.

The film is cheap by Hollywood standards. Gold Derby put its cost at $18 million, so a $20 million start would count as a win. It arrives three weeks before Halloween. Critics have been rough, though. The Hollywood Reporter said it held an 18% approval score on Rotten Tomatoes.

Sony's "The Social Reckoning" earned $650,000 from Thursday previews and was expected to make about $7 million from 2,600 theaters, The Hollywood Reporter said. The film cost $30 million. Aaron Sorkin wrote and directed it. Jeremy Strong plays Mark Zuckerberg, Mikey Madison plays a Facebook whistleblower and Jeremy Allen White plays the reporter she works with. Reviews are mixed.

The original "The Social Network" opened at No. 1 with $22.4 million in 2010 and won Sorkin an Oscar for his script. David Fincher and Jesse Eisenberg did not return for the new film.

Anne Hathaway's "Verity," which opened last weekend, was expected to land in second place with $12 million to $16 million, Gold Derby predicted.

Several smaller films also opened in select theaters, including Alex Gibney's documentary "Musk" and Chris Rock's "Misty Green." Christopher Nolan's "The Odyssey" returned to Imax screens.

Studios will report weekend estimates on Sunday.

What we know: "Other Mommy" leads after strong previews, and "The Social Reckoning" is lagging.
What we don't: Final weekend totals.