LOS ANGELES (Reuters) - The last man on Earth was first at the weekend box office in North America as Will Smith's sci-fi thriller "I Am Legend" crushed the competition with a record opening, said distributor Warner Brothers.

The film brought in $76.5 million and was the seventh consecutive chart-topper for the versatile Smith. It combined with a surprisingly strong $45 million debut for "Alvin and the Chipmunks" to end the box office's five-week losing streak, even as severe winter storms across the Midwest and Northeast hurt ticket sales.

"I Am Legend" ranks as the best December opening of all time, beating the $72.6 million start for "Lord of the Rings: Return of the King" in 2003, the Time Warner Inc-owned studio said. The studio said it had hoped for an opening in the mid-$40 million range.

Smith plays a military virologist who has survived a human-made virus that apparently killed everyone else on the planet. Music video veteran Francis Lawrence directed the film, working from an adaptation of a 1954 novel by Richard Matheson. It was originally envisaged as a vehicle for Arnold Schwarzenegger and director Ridley Scott in the early 1990s.

"Alvin and the Chipmunks" squealed its way to number two with $45 million, more than doubling the expectations of its distributor, Twentieth Century Fox.

The film combines real actors, led by Jason Lee, with animated renderings of Alvin, Simon and Theodore, the beloved helium-voiced singing trio. The News Corp-owned studio said the film played strongly with family audiences, as expected, but also drew plenty of young-adult viewers.

Overall ticket sales rose 36 percent from the same period last year to $163 million, according to tracking firm Media By Numbers. Sales for the year stand at almost $9 billion, a five percent boost from last year, thanks solely to higher ticket prices. Late-fall sales have been soft as films such as incumbent champion "The Golden Compass" and a slew of serious fare like Tom Cruise's "Lions for Lambs" failed to connect with moviegoers.

"The Golden Compass" fell to number three with just $9 million, losing about two-thirds of its opening-weekend audience, one of the biggest slides of the year. In recent weeks, chart leaders have fallen between 40 percent and 50 percent in their second rounds.

New Line Cinema's $180 million family fantasy, starring Nicole Kidman and Daniel Craig, has earned $41 million to date. The struggling Time Warner-owned studio had hoped the film would be the first in a franchise based on British author Philip Pullman's acclaimed children's series "His Dark Materials."

It is doing better overseas but New Line sold the foreign distribution rights to help cover the movie's cost.

Also new was the urban-themed holiday comedy "This Christmas" at number six with almost $3 million. The movie, from closely held Yari Film Group, has earned $3.6 million since opening last Wednesday.

Three days after it scored a leading seven nominations for the Golden Globe Awards, the World War Two-era drama "Atonement" jumped six places to number nine with $1.85 million in its second weekend of limited release. James McAvoy and Keira Knightley picked up nominations for playing lovers torn apart by a family lie and the conflict in Europe.

The film was released by Focus Features, a unit of General Electric Co's NBC Universal.

Thanksgiving champ "Enchanted" fell two to number four with $6.0 million in its fourth week. Walt Disney Pictures' fairy-tale fantasy, starring Globe nominee Amy Adams, has earned $92.3 million to date.

Four-time Globe nominee "No Country For Old Men," which has also topped year-end lists from various critics groups, rose one to number five with $3 million. The gritty Miramax Films drama has earned $33.6 million after a slow rollout over six weeks.

• Will Smith's "I Am Legend" is currently showing at Southside Cinema, St. David's.