Some forecasters had expected the film to make $20m

Tarantino joined with Robert Rodriguez to make the three-and-a-quarter-hour blood-soaked homage to the low-budget horror films of the 1970s.

It debuted at number four with three- day ticket sales of $11.6m (�5.9m) instead of the expected $20m (�10.1m).

Will Ferrell's figure skating comedy, Blades of Glory, topped the chart for a second week, early figures show.

It took receipts of $23m (�11.7m), ahead of animated Meet the Robinsons, about a nerdy orphan who is whisked away to a futuristic world in a time machine, which took $17m (�8.6m).

US/CANADA BOX OFFICE 1) Blades of Glory ($23m) 2) Meet The Robinsons ($17m) 3) Are We Done Yet? ($15m) 4) Grindhouse ($11.6m) 5) The Reaping ($10.1m) 6) 300 ($8.8m) 7) Wild Hogs ($6.8m) 8) Shooter ($5.8m) 9) TNMT ($4.9m) 10) Firehouse Dog ($4m) Source: Media By Numbers

Family comedy Are We Done Yet? was at three with $15m (�7.6m). The film, starring rapper Ice Cube, has earned $19.1m (�9.7m) since opening early on Wednesday.

Hilary Swank horror movie The Reaping opened at number five with $10.1m (�5.14m) for the three days, and $12m (�6.1m) since opening on Thursday.

Grindhouse is a $53m (�27m) double-feature consisting of Rodriguez' zombie thriller Planet Terror and Tarantino's slasher picture Death Proof.

Dimension Films co-chairman Harvey Weinstein told Reuters news agency that he was "disappointed" at the film's performance.

"Are we disappointed about the gross? I'd be lying to you if I said I wasn't. I am disappointed," he said.

Weinstein said the public is always demanding new moviegoing experiences, "and then it takes a while to educate them."

He added: "What Robert and Quentin did was a very noble attempt to re-educate American cinema-goers as to what's good and what was great about seeing those old double bills.

"They tried and the story's not written in one week when you do something this bold."

The two films will be released individually outside the US from 31 May.