Is 3D fatigue starting to set in? DreamWorks’ “How to Train Your Dragon” topped weekend openers with $43.3 million, well behind the $59.3M that “Monsters vs. Aliens” collected exactly a year ago on hundreds of fewer 3D screens, when 3D ticket prices were significantly lower. The “Dragon” take likely wasn’t helped by having to compete with another family-friendly 3D blockbuster, Disney’s “Alice in Wonderland,” which managed an impressive $17.3M during its fourth week and will pass the $300M mark domestically in the next few days.

Despite considerable buzz and an ambitious marketing push by the dying MGM, “Hot Tub Time Machine” opened in third place with a tepid $13.7M, a disappointment after widespread expectations of a bow in the low ’20s. Still, MGM can claim this is the No. 1 non-3D movie in the marketplace, which will remarkably be offering FOUR 3D titles (“Avatar” is around until it bows on DVD in three weeks) with the arrival of Warner Bros.’ hastily converted remake of “The Clash of the Titans” next Friday.