Tom Cruise's action thriller Jack Reacher debuted in second place with a modest $18.9 million debut, according to studio estimates.
Based on the Lee Child best-seller One Shot, the Paramount Pictures release stars Cruise as a lone-wolf ex-military investigator tracking a sniper conspiracy.
It made barely half as much as Cruise's last hit Mission Impossible film Ghost Protocol did in its opening, but cost about $121 million less to make.
"The real winner this weekend might be holiday shopping," said Paul Dergarabedian, an analyst for box-office tracker Hollywood.com.
Opening at number three with US$12 million was Judd Apatow's marital comedy This Is 40, a Universal Pictures film featuring Paul Rudd and Leslie Mann reprising their roles from the director's 2007 hit Knocked Up.
Paramount's road-trip romp The Guilt Trip, featuring Knocked Up star Seth Rogen and Barbara Streisand, debuted weakly at number six with $6.6 million over the weekend.
Studio executives are still hopeful Jack Reacher will fetch a respectable box-office haul.
"Jack Reacher will end up in a very good place. The movie will be profitable for Paramount," said Don Harris, the studio's head of distribution. "The first time I saw the movie I saw dollar signs. It certainly wasn't intended to be compared to a Mission: Impossible, though."
Warner Bros is also hoping for steady crowds for The Hobbit over the next week, despite the debut of two huge newcomers - the musical Les Miserables and the Quentin Tarantino action movie Django Unchained - on Christmas Day.
"We haven't reached the key holiday play time yet," said Dan Fellman, head of distribution for Warner. "It explodes on Tuesday and goes right through the end of the year."
US box-office top 10:
1. The Hobbit: An Unexpected Journey, $44.6 million
2. Jack Reacher, $18.9 million
3. This Is 40, US$12 million
4. Rise of the Guardians, $7.2 million
5. Lincoln, $6.8 million
6. The Guilt Trip, $6.6 million
7. Monsters, Inc $6.1 million
8. Skyfall, $5.7 million
9. Life of Pi, $4.6 million
10. The Twilight Saga: Breaking Dawn - Part 2, $3.2 million
International box-office top 10:
1. The Hobbit: An Unexpected Journey, $110 million
2. Life of Pi, $28.2 million
3. Rise of the Guardians, $16.6 million
4. Skyfall, $10.9 million
5. Wreck-It Ralph, $8.9 million
6. The Twilight Saga: Breaking Dawn - Part 2, $8 million
7. Pitch Perfect, $7.3 million
8. Les Miserables, $5.1 million
9. Love 911, $3.9 million
10. De L'autre Cote du Periph, $3.8 million.
- AP