Yet the general box office was less lively as a flurry of new wide releases did solid to ho-hum business. Overall Hollywood revenues came in at $113.4 million, down 4 percent from the same weekend last year.
Sony scored a one-two punch with "Zombieland" and the animated family tale "Cloudy With a Chance of Meatballs," which took in $16.7 million, slipping to second-place after two weekends at No. 1. The movie raised its domestic total to $82.4 million after three weekends.
Mixing gory action with laughs, "Zombieland" teams Harrelson with Jesse Eisenberg, Abigail Breslin and Emma Stone as a band of humans fighting legions of undead - and taking a road trip to a supposedly zombie-free amusement park.
"What really clicked was the humor of it," said Rory Bruer, head of distribution for Sony. "Truly, there were points in this movie that were so funny, I thought I was going to throw up. I'm serious. It really is a blast."
Taking a big bite of the family audience with $12.5 million was a double-feature reissue of Disney's "Toy Story" and "Toy Story 2" in 3-D, which came in at No. 3. Playing for a limited two-week run, the double-feature sets the stage for the release of "Toy Story 3" in 3-D next year.
The Warner Bros. comedy "The Invention of Lying," with Ricky Gervais and Jennifer Garner, had a soft opening of $7.4 million, finishing at No. 4. Taking place in an alternate reality where everyone tells the truth, the movie stars co-director and co-writer Gervais, who plays a man that discovers how to profit by fibbing.
Fox Searchlight's roller-derby tale "Whip It" - featuring Ellen Page, Juliette Lewis and Drew Barrymore, who also directed - made a weak debut at No. 6 with $4.85 million. The movie casts "Juno" star Page as a beauty-pageant queen who shifts gears to become a roller-derby star.
Female crowds accounted for 70 percent of the audience for "Whip It," according to Fox Searchlight parent 20th Century Fox. Audiences and critics gave the movie high marks, so the studio is hoping it has a longer shelf life than its opening weekend would indicate.
"Like the story, the movie's an underdog, and we think audiences are going to continue to discover it," said Fox distribution executive Chris Aronson.
Tied for sixth-place with $4.85 million was Michael Moore's "Capitalism: A Love Story," which expanded nationwide after a week in limited release. The Overture Films documentary, Moore's exploration of the roots of the economic meltdown, raised its total to $5.3 million.
"Capitalism" played in just 962 theaters, compared to 3,036 for "Zombieland" and about 1,700 cinemas each for "Invention of Lying," "Whip It" and the "Toy Story" movies.
This was Moore's second-best nationwide debut, behind his 2004 sensation "Fahrenheit 9/11," which had a $23.9 million opening weekend.
Overture is counting on "Capitalism" to stick around for an extended box-office run, as did "Fahrenheit 9/11" and other Moore hits such as "Sicko" and "Bowling for Columbine."
"Where most movies are a two-week story, Michael's movies play for a long time," said Kyle Davies, Overture head of distribution.
In limited release, Joel and Ethan Coen's comic drama "A Serious Man" had a big opening with $251,510 in six theaters, averaging a whopping $41,918 per cinema. That compares to an $8,235 average in 3,036 theaters for "Zombieland."
Released by Focus Features, "A Serious Man" follows the domestic and professional troubles of a physics professor in a 1960s Midwest Jewish community.
Lionsgate's basketball documentary "More Than a Game" - which explores the high school years of NBA star LeBron James - opened solidly with $196,681 in 14 theaters, averaging $14,049 a cinema.
Paramount Pictures' fright flick "Paranormal Activity" continued to do strong business, taking in $535,000 from midnight-only screenings in 33 cities. The studio plans to expand the movie to all-hours show times on Friday.
Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Hollywood.com. Final figures will be released Monday.
1. "Zombieland," $25 million.
2. "Cloudy With a Chance of Meatballs," $16.7 million.
3. "Toy Story" and "Toy Story 2" in 3-D, $12.5 million.
4. "The Invention of Lying," $7.4 million.
5. "Surrogates," $7.3 million.
6 (tie). "Capitalism: A Love Story," $4.85 million.
6 (tie). "Whip It," $4.85 million.
8. "Fame," $4.8 million.
9. "The Informant!", $3.8 million.
10. "Love Happens," $2.8 million.