The upstart chiller went into nationwide release and took over the No. 1 spot with $22 million. That compares to just $14.8 million for the debut of Saw VI, a franchise that has been an annual Halloween fixture since 2004.

It was the worst opening ever for Lionsgate's Saw series, whose previous low was $18.3 million for the original movie. Subsequent installments of the Saw franchise all opened at $30 million or better.

This time, horror fans simply gravitated toward Paranormal Activity instead of Saw VI.

"Paranormal ate their lunch," said Paul Dergarabedian, box-office analyst for Hollywood.com. "There's no other way to explain it."

After four weeks in narrower release, distributor Paramount slotted Paranormal Activity into 1,945 theaters. That still was just under two-thirds of the 3,036-theater count for Saw VI. Paramount plans to expand next weekend to an additional 300 to 500 films for Paranormal.

Paranormal Activity raised its total haul to $62.5 million. The low-budget movie was shot for a reported $15,000 but has become a horror sensation because of online fan buzz.

The previous weekend's No. 1 movie, the Warner Bros. tale Where the Wild Things Are, fell to No. 3, just behind Saw VI with $14.4 million. Spike Jonze's adaptation of the beloved children's book by Maurice Sendak raised its total to $54 million.

Among other wide releases, Summit Entertainment's Astro Boy opened at No. 6 with $7 million, Universal's Cirque du Freak: The Vampire's Assistant debuted at No. 8 with $6.3 million and Fox Searchlight's Amelia premiered at No. 11 with $4 million.

Enlarge Paramount Pictures Katie Featherston and Micah Sloat star in Paranormal Activiity, which was No. 1 in the weekend before Halloween.