The psychological thriller, which also stars Muriel's Wedding actress Toni Collette, took $25.8m against The Blair Witch Project's $24.5m between Friday and Sunday, according to industry estimates.

Willis plays a child psychologist in the film about a young boy - played by 11-year-old Haley Joel Osment - who can see, hear and talk to dead spirits around him. The film also stars former New Kids On The Block singer Donnie Wahlberg.

The Blair Witch Project - the low-budget horror film which created a sensation when it went on limited release last month - held steady from the previous week's figures.

Witch fans on Internet

Actor Joshua Leonard in The Blair Witch Project

The mock documentary tells the tale of three student film-makers who vanish in woods near Burkittsville, Maryland, looking for the mysterious Blair Witch.

The film only cost $60,000 to make - but is set to take more than $100m in the US and Canada, and has also spawned many unofficial Websites.

In third place is Julia Roberts' new film, Runaway Bride, with $21m, while Thomas Crown Affair - a remake of the 1968 crime hit starring Steve McQueen and Faye Dunaway - took $14.6m.

The new version stars Pierce Brosnan as Crown - an elegant billionaire - and Rene Russo as Catherine Banning, an investigator who suspects him of stealing a priceless Monet.

Of other new releases, animated film Iron Giant came in at ninth with $5.7m, while Dick, a satire on the Watergate scandal, was 11th with $2.2m - 25 years after Richard Nixon's resignation.