Clooney (centre) plays an ageing football player in 1920s America
George Clooney's latest sports comedy Leatherheads has failed to dislodge gambling film 21 off the top of the North American box office chart.
Clooney's film, a 1920s comedy about American football players, made $13.5m (£6.8m) in its opening weekend - $1.6m (£806,000) less than Las Vegas-set 21.
The film's distributor Universal said it was "disappointed" by the figures.
Jodie Foster's family film Nim's Island made its debut at three with an opening weekend tally of $13.3m (£6.7m).
Animated film Dr Seuss' Horton Hears A Who! dropped two places to four, according to box office tracker Media by Numbers.
Horror movie The Ruins made its debut at five with first weekend takings of $7.8m (£3.9m).
US & CANADA BOX OFFICE
1. 21 - $15.1m
2. Leatherheads - $13.5m
3. Nim's Island - $13.3m
4. Dr Seuss' Horton Hears A Who! - $9.1m
5. The Ruins - $7.8m
Figures for Friday-Sunday
Source: Media by Numbers
Leatherheads, which Clooney directed as well as acted in, had been tipped by its distributor to top this week's chart.
Its failure to do so has been attributed to mixed reviews and a stronger than anticipated showing for Foster's film, which also stars Abigail Breslin of Little Miss Sunshine fame.
"I wish I could have that crystal ball and tell you what went wrong," said Nikki Rocco, head of distribution for Universal.
Leatherheads' lacklustre performance is only the latest setback for Clooney, whose attempt to be credited as its screenwriter was rejected by the Writers Guild of America.
The actor, who claims he rewrote much of Duncan Brantley and Rick Reilly's original script, has downgraded his union membership in protest.
Overall, ticket sales were nearly 30% down on the same weekend last year.