Nicolas Cage (foreground) plays the lead role in World Trade Center

Will Ferrell's motor racing caper took $23m (�12.1m) in its second weekend.

But Stone's film performed better than anticipated, making $19m (�10m) in its first three days on release.

The weekend's biggest surprise, though, was Disney dance movie Step Up, which opened in second place with estimated weekend takings of $21m (�11.1m).

According to studio estimates issued on Sunday, Stone's film has made $26.8m (�14.2m) since its release on 9 August.

NORTH AMERICAN BOX OFFICE 1. Talladega Nights: The Ballad of Ricky Bobby 2. Step Up 3. World Trade Center 4. Barnyard: The Original Party Animals (above) 5. Pulse 6. Pirates of the Caribbean: Dead Man's Chest 7. Zoom 8. The Descent 9. Miami Vice 10. Monster House Source: Exhibitor Relations

The fact-based drama stars Nicolas Cage and Michael Pena as two New York policemen buried alive in the rubble of the Twin Towers after the 9/11 attacks.

Set in a Baltimore high school, Step Up is a teenage romance about a boy from the wrong side of the tracks who becomes the unlikely dance partner of a privileged ballet student.

"It stepped up out of nowhere and surprised everyone," said Paul Dergarabedian of box office analysts Exhibitor Relations. "It was totally unexpected."

Animated comedy Barnyard: The Original Party Animals, last week's number two, fell to four with second weekend takings of $10.1m (�5.3m).

Horror movie Pulse and superhero Spoof were the only other new entries in this week's Top 10, making their debuts at five and seven respectively.