"The Expendables 2" may have knocked out the competition at the box office this weekend, but it didn't pack as much of a punch as Hollywood was expecting.

The sequel featuring a gang of muscular action stars like Arnold Schwarzenegger, Sylvester Stallone and Bruce Willisopened with $28.8 million, according to an estimate from distributor Lionsgate. That was enough to handily beat the weekend's other debuts, including the 3-D animated"ParaNorman," which launched with a so-so $14 million."Sparkle," the inexpensive musical that is Whitney Houston's last film, started off with a respectable $12 million, while the children's movie "The Odd Life of Timothy Green" collected a moderate $10.9 million over the weekend.

While "The Expendables 2" may have claimed the No. 1 position, it failed to meet industry projections that had the movie taking in about $40 million during its opening weekend. The film's disappointing start also falls short of the original's $34.8 million debut in 2010 -- and Lionsgate spent more for the sequel. The studio paid producer Avi Lerner's Millennium Films just under $20 million for rights to distribute the original film in the U.S. and the United Kingdom, but paid $35 million for the same rights to the second movie.

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The good news for Lionsgate is that those who saw the film this weekend enjoyed the movie. Opening weekend crowds assigned it an average grade of A-, according to market research firm CinemaScore, indicating strong word of mouth could help the film reach the $103.1 million domestic gross of the original movie. The audience who saw the sequel this weekend was 63% male, and 65% of the crowd was over the age of 25 -- a slightly older demographic than the original attracted despite the addition of 22-year-old Liam Hemsworth to the new movie's cast.

With few high-profile movie releases slated for the remainder of August, the other three films that hit theaters this weekend will also be banking on strong ticket sales in the weeks to come. Like "The Expendables 2," moviegoers loved "Sparkle," giving it an average A grade -- and "Timothy Green" earned an A-. "ParaNorman" -- which received the strongest critical reviews of any of the four new films -- was given a CinemaScore of B+.

"ParaNorman," about a boy who is able to communicate with the dead, is the second stop-motion movie made by Oregon's Laika Entertainment. The animation house's first production,"Coraline,"opened with a similar $16.8 million in 2009 and went on to become a modest hit, grossing $75.3 million. Laika paid for both the production and advertising costs of "ParaNorman," though it is being released by Universal Pictures' specialty label Focus Features.

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Overseas, the film played in nine foreign markets this weekend and brought in $2 million, raising its international total to $7.6 million. Universal is hoping "ParaNorman" will fare better overseas than "Coraline" did, as the 2009 flick grossed a lackluster $49.3 million abroad.

"Sparkle" is a remake of a 1976 production about a singing girl group that dreams of becoming successful. The new version, set in the 1960s, stars 22-year-old "American Idol"winner Jordin Sparksin her debut film role. This weekend, the movie appealed largely to older women -- many of whom may have been interested in seeing Houston's last on-screen performance. The movie attracted a 74% female crowd, and 62% of the audience was over the age of 35. The movie has a good chance of becoming a success for Sony Pictures, which spent only about $14 million to produce the film.

Walt Disney Studios' "The Odd Life of Timothy Green" also had a small budget -- $25 million. The movie, about two parents who are struggling to conceive a child when a boy magically grows in their backyard, opened Wednesday in an effort to spread positive buzz about the film before the crowded weekend. In its first five days of release, the movie sold $15.2 million worth of tickets.

[Updated, 11:14 a.m. Aug. 19: Like its predecessor, "Step Up Revolution" is faring better internationally than domestically. While the dance film has grossed only $32.9 million in the U.S. and Canada since its release July 27, the 3-D movie has collected $83.4 million abroad. Currently, the film is playing in 33 foreign markets and is performing best in Russia, where it has so far sold $8.1 million worth of tickets. The last installment in the "Step Up" franchise, "Step Up 3-D," grossed $116.9 million abroad -- roughly 73% of its worldwide gross.

Here are the top 10 movies at the domestic box office, according to studio estimates and Hollywood.com:

1. "The Expendables 2" (Lionsgate/Millennium): Opened to $28.8 million.

2. "The Bourne Legacy" (Universal/Relativity): $17 million on its second weekend, down 55%. Domestic total: $69.6 million. $18.2 million overseas in 18 foreign markets. International total: $28.1 million.

3. "ParaNorman" (Focus/Laika): Opened to $14 million. $2 million overseas in nine foreign markets. International total: $7.6 million.

4. "The Campaign" (Warner Bros.): $13.4 million on its second weekend, down 50%. Domestic total: $51.7 million.

5. "Sparkle" (Sony): Opened to $12 million.

6. "The Dark Knight Rises" (Warner Bros./Legendary): $11.1 million on its fifth weekend, down 41%. Domestic total: $409.9 million.

7. "The Odd Life of Timothy Green" (Disney): Opened to $10.9 million on its first weekend, $15.2 million since its Wednesday debut. 

8. "Hope Springs" (Sony/MGM/Mandate): $9.1 million on its second weekend, down 38%. Domestic total: $35.1 million.

9. "Diary of a Wimpy Kid: Dog Days" (Fox): $3.9 million on its third weekend, down 52%. Domestic total: $38.8 million. $866,815 overseas in five foreign markets. International total: $8.8 million.