Updated

CHICAGO-- There was no stopping "Limitless" at the box office.

The sci-fi thriller opened at No. 1 this weekend with $19 million, according to studio estimates Sunday.

The film from Relativity Media stars Bradley Cooper as a struggling writer who takes a magical pill that allows him to tap into his maximum brain potential. Suddenly he's cleaned up, making millions and wowing everyone he meets. Robert De Niro co-stars as a financial guru who's fascinated by him, with Abbie Cornish as Cooper's skeptical girlfriend.

"Limitless" broke out of a crowded pack of new releases and holdovers to take the top spot.

Last week's No. 1, the alien invasion movie "Battle: Los Angeles," fell to third place with $14.6 million. The Sony Pictures release has now made an estimated $60.6 million in two weeks.Coming in second was the animated Western "Rango," featuring the voice of Johnny Depp as a chameleon who's stuck in the desert. The Paramount film made $15.3 million for a three-week total of nearly $92.6 million.

It was a slow weekend, with the other new releases battling for the fourth and fifth spots. At No. 4 was the Lionsgate thriller "The Lincoln Lawyer" starring Matthew McConaughey as a sleazy defense attorney on a high-profile case. It made an estimated $13.4 million. In fifth place was "Paul," with Seth Rogen providing the voice of a pot-smoking, wise-cracking alien who befriends a couple of British sci-fi geeks, played by Simon Pegg and Nick Frost (who also wrote the script). The Universal Pictures comedy made about $13.2 million.

Kyle Davies, Relativity's president of theatrical distribution, said he thinks "Limitless" stood out this weekend through a combination of its marketing message and good word of mouth.

"This was a thriller but a very different kind of thriller," he said. "It was a unique angle on a traditional genre."

Davies also pointed to Cooper's appeal as a factor in the film's success. "Limitless" allowed the star of "The Hangover" and "The A-Team" to show a more dramatic side.

"He's coming into his own as a leading man. I think he appeals to men and women," he said. "And De Niro is just awesome in this."

The simple tagline on the film's posters -- "What if a pill could make you rich and powerful?" -- went a long way in luring audiences, said Hollywood.com analyst Paul Dergarabedian: "The art of the tagline has sort of been lost and this brought it back."

And certainly the front-and-center presence of the blue-eyed Cooper, who's also an executive producer on the film, didn't hurt.

"He could be America's new leading man," Dergarabedian said. "He can do comedy, he can do action, he can do drama. Women love to look at him and guys want to have a beer with him. But he's no overnight star -- he's been around for a while."

On the other end of the success spectrum is "Mars Needs Moms!" which came in eighth place this week with just $5.3 million. The 3-D animated adventure movie from Disney, about a little boy who follows his mom when aliens kidnap her and take her to Mars, cost an estimated $150 million to make. It's only grossed about $15.4 million in two weeks and has just 38 percent positive reviews on the Rotten Tomatoes website.

"It's inexplicable," Dergarabedian said. "Families need entertainment, so if a new family film comes out -- whether it's `Rango' following `Gnomeo & Juliet' or `Mars Needs Moms!' following `Rango,' you figure they're going to see it."

"I don't think people stayed away from `Mars Needs Moms!' because it's in 3-D," he added. "This is not a referendum on 3-D."

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Hollywood.com. Final figures will be released Monday.

1. "Limitless," $19 million.
2. "Rango," $15.3 million.
3. "Battle: Los Angeles," $14.6 million.
4. "The Lincoln Lawyer," $13.4 million.
5. "Paul," $13.2 million
6. "Red Riding Hood," $7.3 million.
7. "The Adjustment Bureau," $5.9 million
8. "Mars Needs Moms!" $5.3 million.
9. "Beastly," $3.3 million.
10. "Hall Pass," $2.6 million.