"Tron: Legacy," a costly 3D sci-fi movie that Walt Disney Co has promoted for more than three years, opened disappointingly at the weekend box office in North America, while a new comedy starring Reese Witherspoon was one of the biggest flops of the year.

The "Tron" movie, a massively hyped sequel to an obscure 1982 movie, earned $43.6 million during its first three days of release, Disney said Sunday. Industry observers had been expecting a three-day start in the $50 million range, although Disney said the opening was within its own expectations.

The effects-laden update reportedly cost $170 million to make, and more than $100 million to market worldwide. Disney never divulges budgets.

Internationally, the film earned a modest $23 million from No. 1 openings in all 26 of its markets, including Japan, Australia, Britain and Brazil. These markets represent about half of the international sales pie.

Meanwhile "How Do You Know" opened at No. 8 with just $7.6 million in the United States and Canada, far short of modest expectations in the $12 million range. The Columbia Pictures project cost about $100 million to make, with half the budget spent on salaries for Witherspoon, co-stars Jack Nicholson, Owen Wilson and Paul Rudd, and writer/director James L. Brooks. Extensive reshoots also drove up costs.

Executives at the Sony Corp unit were despondent about the opening, although the film had suffered bad buzz for some time with no help from a forgettable title.

"YOGI" BARELY AVERAGE

A third newcomer did not do much better. "Yogi Bear," a live-action/animated update of the old television cartoon, came in at No. 2 with $16.7 million. Distributor Warner Bros. said it had hoped for an opening between $18 million and $20 million, but the Time Warner Inc unit expected the Christmas holiday would boost business. The $80 million film stars Dan Aykroyd as the voice of the title character and Justin Timberlake as his sidekick Boo Boo.

Critics trashed all three films, which vied for the attention of holiday-distracted moviegoers alongside national expansions of acclaimed awards-season contenders Paramount Pictures' "The Fighter" (No. 4, $12.2 million) and Fox Searchlight's "Black Swan" (No. 7, $8.3 million).

Last weekend's champion, 20th Century Fox's "The Chronicles of Narnia: The Voyage of the Dawn Treader," fell to No. 3 with $12.4 million in its second weekend.

"The Tourist," a widely mocked caper starring Angelina Jolie and Johnny Depp, dropped three places to No. 5 with $8.7 million, also in its second weekend. The Columbia release tied with Disney's former chart-topping cartoon "Tangled."

The final weekend before Christmas is traditionally slow, although films often enjoy long runs as school holidays start to take effect. But overall business has been weak for some time, with year-on-year sales down for six weekends in a row.

"A malaise has crept over the marketplace," said Paul Dergarabedian, head box office analyst at Hollywood.com. "The lack of momentum is hurting everybody across the board."

But Disney was bullish about "Tron: Legacy," a project that has occupied the attention of two regimes at the studio in recent years. It has been offering tantalizing glimpses to movie fans at the annual Comic-Con convention since 2008, and raised the heat in recent months with cross-marketing efforts across its theme parks, consumer-products and cable TV wings.

Jeff Bridges returns to "Tron" as a videogame developer trapped in a virtual environment called the Grid. While the original film appealed only to male youngsters, Disney targeted the reboot at men and women of all ages.

But exit polling indicated the film skewed to men aged 18 to 30, with relatively little interest in mainstream multiplexes. Instead, the film's tech-savvy constituency thronged 3D and big-screen theaters. About one-quarter of sales -- $10.3 million -- came from Imax Corp's 234 screens. The film played in almost 3,500 theaters overall.