For the third week in a row, The Avengers dominated the box office. Marvel’s superheroes added another $55 million to their domestic total – putting the film over $450 million in a record-breaking seventeen days. Meanwhile, the three new releases that lined up to challenge The Avengers all struggled in the blockbuster’s wake.

It didn’t claim the record for highest debut or the greatest attendance, but this year’s Super Bowl weekend still caught most box office watchers by surprise with two bigger-than-expected openings. Fox’s Chronicle was first with $22 million from 2,907 locations, but CBS Films’ The Woman in Black was right on its heels with $21 million from 2,855. That’s the first time that two titles have opened to over $20 million on a Super Bowl frame since… ever.

On Easter weekend the animated hit Rio managed to hold on to its number one perch for a second weekend in a row with an estimated $26.8 million.  The padding between Fox’s birds and the Tyler Perry’s bawd was pretty slim, however.  In second place Madea’s Big Happy Family was right behind Rio with an estimated $25.8 million.

After finishing in first on Friday, The Rite stayed on top with a three day estimate of $15 million from its 2,985 locations.  No Strings Attached followed in second place, holding on to 58% of its first weekend total.  The Mechanic opened in third for the weekend with $11.5 million, a figure that was well above most projections for the R-rated action film.

With some of the lowest totals I’ve seen since, um, Labor Day; Columbus Day 2010 got off to a weak start at the box office. Sure, The Social Network made a good showing in its second week, falling just 31% to push Life as We Know It into second place – but those two films combined could not match last year’s single debut Couple’s Retreat. Meanwhile Disney’s Secretariat stumbled badly, coming in a distant third in a race they hoped to win.

With only days left in the summer movie season, a stunning five new releases elbowed their way into theatres this weekend. And not one was a match for The Expendables. Sylvester Stallone’s testosterone parade easily held its place at number one for its second weekend; earning an estimated $16.5 million and bringing its new domestic cume to $64.8 million.

You know it’s a slow weekend when both wide-release debuts fail to break $13 million. The under performance of The Back-Up Plan and The Losers left room enough for How to Train Your Dragon to take number one with $15 million – the lowest grossing weekend for a top-ranked movie so far this year. It’s doubtful that CBS Films will find a way to doctor those Back-Up Plan numbers by Monday so maybe, just maybe, the slow-to-start 3D Dragon will get to stay on top?

Two films that got bounced around on their respective distributor’s release schedules finally debuted this Friday. What a shocker that neither one exactly set the box office on fire! The “hilarious” invitro-fertilization comedy The Back-Up Plan gets to take Friday bragging rights for CBS Films with $4.2 million from 3,280 locations (though that total is nothing to brag about). WB’s comic-adaptation The Losers is off to a disappointing start at number four with just $3.2 million from 2,936 dates. By Sunday, however, both new films will likely be trumped by the fifth (!) weekend of How to Train Your Dragon. Last weekend Dragon had its weekend crown stripped by the Thursday-enhanced figures of Kick-Ass. Lionsgate’s longed-for PR boost never materialized, however, and the ass-kicking is now down over 62% entering week two. What weird twist will make this weekend confusing at the box office?  Check back tomorrow to find out.

Opening this weekend is the Jennifer Lopez & Alex O’Loughlin romantic comedy The Back-up Plan.   To help promote the film, I recently got to interview the two stars as a reporter for our partners at Omelete.  While I wasn’t sure what to expect when I sat down to do the interview, I’ll admit it turned out a lot better than I expected.  Also, the interview featured a lot of laughter.  Perhaps it was due to the questions I asked from the people that follow me on Twitter.  But more than likely, it was a combo between the questions and good luck.  Trust me, JLo was a lot funnier than I expected and I promise she’ll make you laugh as you watch.  We even talked about Anaconda.  I couldn’t believe it.  Hit the jump for the interview and more on The Back-up Plan: