NEW YORK — “Thor: Ragnarok” thundered to one of the year’s best box-office debuts with an estimated $121 million domestically, proving again the might of the Walt Disney Co.

The robust debut for Marvel’s third “Thor” movie was a welcome shot in the arm for Hollywood and theater owners who have suffered through a terrible October at the box office. “Thor: Ragnarok” also bucked the trend of diminishing returns for sequels. The 2011 “Thor” debuted with $65.7 million; 2013’s “Thor: The Dark World” opened with $85.7 million.

“In this business, it’s not often you see the second and third installments in the franchise outpacing the previous issue,” said David Hollis, Disney’s distribution chief. “You don’t expect never-ending returns when it comes to sequels, but it definitely speaks to the quality of the talent at the Marvel Studios team and the way they’re thinking about each film out of the gate.”

The weekend’s other new nationwide release, STX Entertainment’s “A Bad Moms Christmas,” opened with $17 million over the weekend and $21.6 million since opening Wednesday. The holiday-themed sequel, which returns stars Mila Kunis, Kristen Bell and Kathryn Hahn, came in shy of the 2016 original’s $23.8 million opening.

But the big story was “Thor,” which also grossed $151.4 million in its second week of international release.