The Warner Bros. adventure debuted with $55.55 million in North American ticket sales, according to studio estimates Sunday - the biggest October opening ever and the biggest openings for Bullock and Clooney.
"It's all good news," said Dan Fellman, Warner Bros. president of domestic distribution.
He credited director and co-writer Alfonso Cuaron, who takes viewers into orbit with a film that's set almost entirely in space and explores the challenges faced by two astronauts during a spacewalk. Cuaron's team developed equipment and technology to replicate the weightlessness of space.
"It's never been seen before, visual effects like this," Fellman said. "Just the space shots are mind-boggling. It looks like you're right there."
Last week's top movie, Sony's "Cloudy with a Chance of Meatballs 2," rolled into second place with $21.5 million. The animated sequel features the voices of Bill Hader and Anna Faris and a cast of "foodimals," like tacodiles and shrimpanzees.
R-rated fare rounds out the top six. Twentieth Century Fox's "Runner Runner," starring Ben Affleck and Justin Timberlake, opened in third place with $7.6 million.
Warner Bros.' "Prisoners," starring Hugh Jackman and Jake Gyllenhaal, crept into the fourth spot. Universal's racing tale "Rush," starring Chris Hemsworth, drove into fifth place, followed by "Don Jon," Joseph Gordon-Levitt's directorial debut about a porn addict looking for love.
"The adult drama is back, and fall is the season for the adult drama," said Paul Dergarabedian, senior media analyst for box-office tracker Rentrak. "This is when you get your more challenging films, some of the more esoteric fare, and a lot of those movies, by their nature, have to be rated R."
Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Rentrak. Final domestic figures will be released Monday.
1. "Gravity," $55.55 million.
2. "Cloudy with a Chance of Meatballs 2," $21.5 million.
3. "Runner Runner," $7.6 million.
4. "Prisoners," $5.7 million.
5. "Rush," $4.8 million.
6. "Don Jon," $4.16 million.
7. "Baggage Claim," $4.12 million.
8. "Insidious Chapter 2," $3.87 million.
9. "Pulling Strings," $2.5 million.
10. "Enough Said," $2.15 million.
Follow AP Entertainment Writer Sandy Cohen at http://www.twitter.com/APSandy .
Universal and Focus are owned by NBC Universal, a unit of Comcast Corp.; Sony, Columbia, Sony Screen Gems and Sony Pictures Classics are units of Sony Corp.; Paramount is owned by Viacom Inc.; Disney, Pixar and Marvel are owned by The Walt Disney Co.; Miramax is owned by Filmyard Holdings LLC; 20th Century Fox and Fox Searchlight are owned by News Corp.; Warner Bros. and New Line are units of Time Warner Inc.; MGM is owned by a group of former creditors including Highland Capital, Anchorage Advisors and Carl Icahn; Lionsgate is owned by Lions Gate Entertainment Corp.; IFC is owned by AMC Networks Inc.; Rogue is owned by Relativity Media LLC.