The film, a Blair Witch-style first-person POV account of a monster attack on New York that was produced by JJ Abrams and directed by Matt Reeves, took nearly twice as much as Fox's new romantic comedy 27 Dresses.
Cloverfield relied on a successful viral campaign to spread word of its approach after the studio planted teaser footage on the internet late last year.
The film's excellent launch powered the overall weekend box office as the top 12 films grossed $135.3m and performed 39% ahead of the same weekend last year.
27 Dresses opened in second place on $22.4m; it stars Katherine Heigl as an eternal bridesmaid who harbours romantic feelings for her sister's fiance. Ed Burns and Malin Akerman round out the key cast.
Warner Bros' tearjerker The Bucket List fell to third in its fourth weekend on $15.2m for $42.7m, while Fox Searchlight's Juno remained on course to cross $100m after adding $10.3m for $85.4m. The hit comedy ranks fourth in its seventh weekend and stands a good shot at crossing $100m by the end of next weekend if it receives a timely boost when the Oscar nominations are announced on Tuesday [Jan 22].
Buena Vista's adventure sequel National Treasure: Book Of Secrets is on the cusp of $200m and ranks fifth on $198m after five.
Overture Films' maiden release Mad Money opened in seventh place on $7.7m. The comedy stars Diane Keaton, Katie Holmes and Queen Latifah as Federal Reserve employees who plot to steal cash that is about to be destroyed.
Overture's president of worldwide marketing, distribution and new media Peter Adee was upbeat about the launch and said the film was expected to take $9.3m over the four-day Martin Luther King holiday and would continue to play well in mid-week with the mature female and male crowd and should finish on around $25m.
'We feel pretty good,' Adee said. 'We opened the movie against some pretty stuff competition and ultimately we are going to be profitable.'
Adee said the company paid a little over $5m for rights and expected strong home entertainment and ancillary performance.
Focus Features' Atonement remained in 10th place and added $4.8m for $31.9m in the seventh weekend.
'It clearly shows that the Golden Globes are very significant in the US box office, particularly with a film like this and we're delighted,' Focus' domestic distribution chief Jack Foley said. 'If the ceremony had been televised it would have done even better.' Atonement won Globes for best drama and score last weekend.
Next weekend's wide release Fox's comedy Meet The Spartans; Lionsgate's action saga Rambo starring Sylvester Stallone; Paramount Vantage's Sundance 2007 dance film pick-up How She Move; and Sony's cyberthriller Untraceable starring Diane Lane. Warner Bros will expand its legal thriller Michael Clayton starring George Clooney, Tilda Swinton and Tom Wilkinson.
Estimated Top 10 North America Jan 18-20, 2007
Film (Dist)/Int'l dist/Est wkd gross/Est total to date
1 (-) Cloverfield (Paramount) PPI $41m -
2 (-) 27 Dresses (Fox) Fox Int'l $22.4m -
3 (1) The Bucket List (Warner Bros) WBPI $15.2m $42.7m
4 (3) Juno (Fox Searchlight) Fox Int'l $10.3m $85.4m
5 (4) National Treasure: Book Of Secrets (Buena Vista) WDSMPI $8.1m $198m
6 (2) First Sunday (Screen Gems) SPRI $7.8m $28.5m
7 (-) Mad Money (Overture Films) Millennium Films $7.7m -
8 (5) Alvin And The Chipmunks (Fox) Fox Int'l $7m $196.4m
9 (6) I Am Legend (Warner Bros) WBPI $5.1m $247.7m
10 (10) Atonement (Focus Features) $4.8m $31.9m