By Joshua Rich
Updated March 22, 2009 at 09:44 PM EDT

What started as a close and unpredictable race to box office supremacy wound up an easy win for Nicolas Cage’s latest sci-fi flick, Knowing, which grossed $24.8 mil this weekend, trumping challenges from the hearty laugher I Love You, Man and the Julia Roberts-Clive Owen rom-thrill Duplicity.

While I’m somewhat surprised by the outcome — Knowing fared much better than I, or most other box office prognosticators, expected — in the end the battle wasn’t even very close. Cage scored his third consecutive No. 1 opening in the past year and a half, drawing a diverse crowd that was evenly divided between men and women and about two-thirds over the age of 25. For indie distributor Summit, meanwhile, Knowing‘s debut marks a second big win after last fall’s Twilight (which happened to hit DVD this weekend, in case you didn’t hear — yay!).

I Love You, Man was a solid second-place finisher, grossing $18 mil and cementing Paul Rudd’s status as a rising comedy draw. While perhaps a bit lower than hoped, the film’s opening sum is on par with that of Rudd’s last success, Role Models ($19.2 mil), which wound up banking $67.3 mil during its domestic run. With an audience that basically hits “all four quadrants” (young and old, male and female) awarding the film a decent B+ CinemaScore grade, I Love You, Man could have some box office legs in the weeks to come.

The same can’t be said about Duplicity (No. 3), which disappointed with $14.4 mil, despite boasting some pretty big names. It’s hard to compare the film’s performance to that of any recent Julia Roberts release — simply because the woman still often dubbed the biggest female star in the world hasn’t had a lead role in a major movie in years. That said, this opening total falls well short of the $20 mil-to-$40 mil premieres she consistently drew during her heyday from 1997 to 2001. And with a woeful CinemaScore grade of C from a “one quadrant” crowd mostly comprised of older women, Duplicity doesn’t appear to be the comeback hit many hoped it would be.

Race to Witch Mountain (No. 4 with $13 mil) and Watchmen (No. 5 with $6.7 mil) rounded out the top five in a frame whose overall gross declined about 5 percent from a year ago, making this the second “down” weekend in a row. But the slow times shouldn’t last much longer, as Monsters vs. Aliens is set to scare up a fortune starting next weekend.