“I Am Legend” looks like the best opening of Will Smith’s storied career, with Steve Mason at Fantasy Moguls projecting a whopping $73.3 million for its first three days, which would make it the sixth biggest opening of 2007. The modestly budgeted animated “Alvin and the Chipmunks” exceeded expectations even more, and Mase thinks it will end up with $38.4 by Sunday night, exceeding the opening of the much-touted “Bee Movie.” Last week’s leader, “The Golden Compass,” plummeted 61 percent from its poor opening and should start disappearing from the nation’s screens by next Friday, when five new wide openings arrive. On the limited front, the little comedy that could, “Juno,” expanded to 40 location and proportionally beat the pants off “Atonement,” expanding to 117 screens, with a whopping $35,000 per venue for “Juno” versus $4,118 per location for Golden Globe nominations leader “Atonement.” The heavily publicized “The Kite Runner” at 35 venues got off to a relatively soft start with $15,000 per and Francis Coppola’s first flick in 10 years, “Youth Without Youth,” was DOA with $4,296 per at six venues.