Alfonso Cuarón's 3-D sci-fi drama "Gravity" shot to the top of the box-office charts on Friday with more than $17.5 million in ticket sales, according to estimates.

The story of two stranded astronauts starring Sandra Bullock and George Clooney, "Gravity" is one of the top-reviewed movies of the year with a 98% positive rating on the fim review aggregation site Rotten Tomatoes. To open his review, L.A. Times film critic Kenneth Turan wrote: "'Gravity' is out of this world."

Filled with head-spinning action depicting outer space action and weightlessness, the film is Cuarón's first since "Children of Men" from 2006. That film, despite critical raves and three Oscar nominations, took in only $35.6 million at the domestic box office. "Gravity" is expected to exceed that number in its opening weekend.

The weekend's other debut, the Justin Timberlake and Ben Affleck-led "Runner Runner," opened with an estimated $2.7 million on Friday and is on track for third place. The story of a college student (played by Timberlake) who gets tangled with an online gambler (Affleck), the film has earned mostly negative reviews. Its 8% score on Rotten Tomatoes is among the season's lowest.

Tracking for second place for the weekend, the animated film "Cloudy with a Chance of Meatballs 2" earned an estimated $4.7 million on Friday. Rounding out the top five, "Prisoners" earned an estimated $1.7 million and "Don Jon," written and directed by star Joseph Gordon-Levitt, earned $1.4 million.

'Gravity' makes one giant leap with record box office
Fueled by the strongest reviews of the year, Gravity hit the stratosphere at the box office this weekend, running rings around the latest thriller from Ben Affleck and Justin Timberlake.

The Sandra Bullock outer space saga collected $55.6 million, a record in October, according to studio estimates.

The haul easily eclipsed analysts' projections of $35 million, and its near-unanimous positive reviews, analysts say, make it an early frontrunner in the awards race.

Propelling sales: IMAX theaters, which accounted for $11.2 million, the biggest October opening for any film in the colossal format. Company CEO Greg Foster says that the bulk of the nation's 425 IMAX theaters have booked Gravity for the next month.

"We have a special relationship with space films, beginning with our documentaries, and this is the kind of quality movie our audience expects," he says.

3-D acquitted itself well, too, as it accounted for 80% of ticket sales, according to distributing studio Warner Bros. Gravity eclipsed the October debut record of Paranormal Activity 3, which opened to $52.5 million in 2011.

The film earned an astounding thumbs-up from 98% of the nation's critics, according to survey site Rottentomatoes.com.

Fans were nearly as over the moon: 91% of moviegoers said they enjoyed the movie, directed by Alfonso Cuaron and co-starring George Clooney. Nearly 60% of the audience was 35 and over, and the movie scored an A- with moviegoers, according to pollsters CinemaScore.

Tim Briody of Boxofficeprophets.com says that Gravity had no trouble hitting the box office stratosphere despite the unpredictable nature of science fiction films — particularly original ones.

But the $100 million picture managed to combine "incredible effects, horror movie-style vibe (seriously, try and watch any scene from it without wanting to hold your breath), an A-list cast and ridiculously positive word-of-mouth to set everything up properly for the largest opening in months."

And it gives the fall season, which often sees sluggish ticket sales until Thanksgiving, critical momentum as studios try to catch last year's ticket sales pace.

"The real question at this point is how high it can go," says Ray Subers of Box Office Mojo.

Gitesh Pandya of Boxofficeguru.com says that Gravity drew non-sci-fi fans in part with its high-powered stars, particularly Bullock, who has discovered 2013 is her lucky number. Earlier this year, her comedy The Heat opened to $39 million on its way to $159 million. Both Bullock and Clooney scored the highest debuts of their career this weekend.

"Bullock remains a major star, very likable, and very bankable," Pandya says.

Affleck and Timberlake couldn't find their way to the bank this weekend as their crime thriller Runner Runner fell well below expectations. The only other newcomer of the weekend — which scored a miserable 8% approval rating among critics, Rottentomatoes.com says — mustered only $7.6 million, good for third place.

The animated comedy Cloudy with a Chance of Meatballs 2 took second place with $21.5 million, while the drama Prisoners took fourth with $5.7 million.

The Ron Howard racing film Rush rounded out the top five with $4.4 million. Final figures are due Monday.