As expected, “Avatar” led the box-office by a wide margin during its fourth weekend, with Fox reporting an astounding estimated $48 million in North America — and a whopping $1.34 billion cume worldwide, second on the all-time list only to James Cameron’s last picture “Titanic” ($1.8B in 1997-8 dollars). The best any of the three newcomers could manage was the apparent fourth-place finish of “Daybreakers,” with Lionsgate reporting an estimated $15M. That placed the horror flick behind a pair of holdovers: Warners’ “Sherlock Holmes” and Fox’s “Alvin and the Chipmunks: The Squeakquel,” which landed in a virtual tie for second place with their respecive studios estimating $16.6M and $16.3M (tomorrow’s “actual” numbers could well re-sort the 2-4th place finishes). Universal’s run of bad luck continued with the rom-com “Leap Year,” which failed by an estimated $1 million to even make it into the double digits, DOA in sixth place behind the studio’s underperforming and pricey “It’s Complicated.” Despite critical hosannahs, “Youth in Revolt” could scrape up no more than an estimated $7 million in ninth place, ironically helping to push its poorly-reviewed (and far costlier) Weinstein Co. stablemate “Nine” out of the top ten. It seems clear that Michael Cera is no more of a box-office draw than his “Juno” co-star Ellen Page, whose “Whip It” tanked last fall, even with solid notices.