‘Thor: Ragnarok’ rumbles to $121M box office debut

NEW YORK – “Thor: Ragnarok’’ thundered to one of the year’s best box-office debuts, opening with an estimated $121 million in North American theatres. The robust debut for the third “Thor’’ movie was a welcome shot in the arm for Hollywood and theatre owners who have just 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.

The big opening cements the unlikely breakthrough of New Zealand director Taika Waititi, who shepherded the $180 million production to Marvel’s best reviews since 2008’s “Iron Man.’’

The weekend’s other new nationwide release was the holiday-themed comedy sequel “A Bad Mom’s Christmas.’’ It grossed $17 million over the weekend.