Last week's leader added an estimated $15.1m to reach $46.5m in an uninspiring session that bore all the hallmarks of the dead zone that precedes the Memorial Day start of the summer season in the first weekend of May.
Leatherheads, a period caper about an American football coach and his star player who wrestle for the affections of a reporter, launched in second place on $13.5m, edging out Nim's Island in third on $13.3m. Final figures will be posted on Monday.
Clooney, Renee Zellweger and John Krasinski from the US version of hit TV series The Office round out the key cast. This marked Clooney's third directorial outing after Confessions Of A Dangerous Mind and Good Night, And Good Luck.
He also claimed to have rewritten Duncan Brantley and Rick Reilly's 17-year-old screenplay but has had a hard time convincing the Writers Guild Of America (WGA) of this.
As a result, it emerged late last week that Clooney voluntarily downgraded his union membership last year in a move that is known as going 'financial core'. He will pay slightly lower subscription rates and loses his eligibility to vote in WGA matters in a move that is apparently irreversible. He kept the spat quiet until now so as not to distract parties from the recent WGA contract talks.
Nim's Island stars Abigail Breslin as a youngster who inhabits a Pacific island and sends an SOS to her favourite author, an agoraphobic city dweller played by Jodie Foster, when her father goes missing. Gerard Butler also stars.
Paramount's horror release The Ruins - an unequivocal travel advisory against the perils of walking off the beaten path - opened in fifth place on $7.8m and stars Jonathan Tucker.
Elsewhere. the latest Dr Seuss adaptation, Horton Hears a Who! came in fourth place added $9.1m for $131.1m, while a host of underperformers from recent weeks began their steady slide out of the top 10.
Superhero Movie ranks sixth on $16.9m after two weeks on release, Drillbit Taylor in eighth place has grossed $25.6m after three and 10,000 B.C. ranks 10th on $89.3m after five.
Next weekend's wide releases are Sony's horror flick Prom Night starring Jamie Lee Curtis; Miramax Films' Smart People with Dennis Quaid, Sarah Jessica Parker and Ellen Page; and Overture Film's well-received festival hit The Visitor with Richard Jenkins.
Estimated Top 10 North America Apr 4-6, 2008
Film (Dist)/Int'l dist/Est wkd gross/Est total to date
1 (1) 21 (Sony) SPRI $15.1m $46.5m
2 (-) Leatherheads (Universal) UPI $13.5m -
3 (-) Nim's Island (Fox) Summit Entertainment $13.3m -
4 (2) Dr Seuss' Horton Hears a Who! (Fox) Fox Int'l $9.1m $131.1m
5 (-) The Ruins (Paramount) PPI $7.8m -
6 (3) Superhero Movie (MGM) TWC $5.4m $16.9m
7 (4) Tyler Perry's Meet The Browns (Lionsgate) $3.5m $37.8m
8 (5) Drillbit Taylor (Paramount) PPI $3.5m $25.6m
9 (6) Shutter (Fox) Fox Int'l $2.9m $23.2m
10 (7) 10,000 BC (Warner Bros) WBPI $2.8m $89.3m