An elite squad of guinea pigs has worked its own brand of magic at the box office, taking the No. 1 spot from boy wizard Harry Potter.

The 3-D "G-Force" was the top movie at the box office this weekend, opening with $32.2 million, according to studio estimates Sunday. The Walt Disney release from producer Jerry Bruckheimer, with its mixture of live action and computer-generated animation, is a "Mission: Impossible"-style adventure. It features voiceover work from Nicolas Cage, Sam Rockwell, Tracy Morgan and Penelope Cruz as resourceful rodents.

Last week's No. 1 film, "Harry Potter and the Half-Blood Prince," came in a close second with an estimated $30 million. That's a whopping 61-percent drop from its huge opening last weekend of $79.5 million.

Coming in third was another of the week's wide releases, the battle-of-the-sexes romantic comedy "The Ugly Truth," which had a $27 million opening.

The sixth installment in the Harry Potter franchise has now made $222 million total, which is $14 million ahead of where part five, "Harry Potter and the Order of the Phoenix," was after 12 days in theaters in 2007. And this week, "Half-Blood Prince" will start showing on 166 IMAX screens, which the last "Harry Potter" movie did from the start.

"So we're coming in with this one (in IMAX) a little bit late, but it's going to be a great addition and it'll keep our momentum going," said Dan Fellman, Warner Bros.' head of distribution.

"G-Force" triumphed in a crowded summer marketplace with its combination of 3-D effects and the Disney and Bruckheimer brands, said Mark Zoradi, president of Disney's motion-picture group.

"You never go into a situation where you're competing against two important movies — the second weekend of 'Harry Potter' and the opening weekend of 'The Ugly Truth' — you never go in cocky," Zoradi said.

The one-two of PG-rated movies reinforces the fact that summer is prime family movie time, said Paul Dergarabedian, box-office analyst for Hollywood.com.

"This summer is all about packaging and escapism," Dergarabedian said of the strong showing for "G-Force." "People were scratching their heads and dragging their kids to go see this thing. They were watching the trailers with absolute shock going, 'Is that really happening?' But as a kid you're like, 'I gotta go see it.' This is a testament to the fact that Jerry Bruckheimer, like ['Transformers' director] Michael Bay, knows exactly what summer movie audiences want."

With $27 million, "The Ugly Truth" performed at the high end of Sony Pictures' expectations, said head of distribution Rory Bruer.

"The chemistry between Katherine Heigl and Gerard Butler is a blast. It's really a lot of fun, everything we'd hoped it would be," Bruer said. "From sneak previews to word-of-mouth screenings we had on the movie, we knew people liked the movie."

Critics weren't so enamored, though: "The Ugly Truth" received just 15 percent positive reviews on the Rotten Tomatoes Web site.

"If I have a choice of deciding between what the audience's opinion is going to be versus the critics', I'll definitely go with the audience's every day, and they spoke loud and clear," Bruer said.

Also opening nationwide this weekend was another Warner Bros. release, the horror movie "Orphan," about a couple who adopts a little girl who's not nearly as sweet as she seems. It came in fourth place with $12.8 million.

Expanding in its second week of limited release, the Fox Searchlight romantic comedy "500 Days of Summer" made $1.63 million. Going from 27 screens to 85, it's grossed just over $3 million. The critical hit stars Joseph Gordon-Levitt and Zooey Deschanel in an out-of-order tale of boy-meets-girl.

On the other end of the cinematic spectrum, the dominant movie of the summer, "Transformers: Revenge of the Fallen," is now the 10th-highest grossing film of all time with just over $379 million. The Paramount sequel made $8 million this weekend, pushing it past 2003's "The Lord of the Rings: The Return of the King," which made just over $377 million.

Dergarabedian said movies like "Transformers," "Harry Potter" and the R-rated, surprise-hit comedy "The Hangover," which has now made over $247 million, have kept this summer's revenues right in line with 2008, when "The Dark Knight" was all the rage.

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

1. "G-Force," $32.2 million.

2. "Harry Potter and the Half-Blood Prince," $30 million.

3. "The Ugly Truth," $27 million.

4. "Orphan," $12.8 million.

5. "Ice Age: Dawn of the Dinosaurs," $8.2 million.

6. "Transformers: Revenge of the Fallen," $8 million.

7. "The Hangover," $6.5 million.

8. "The Proposal," $6.4 million.

9. "Public Enemies," $4.2 million.

10. "Bruno," $2.7 million.