Age of Ultron wasn't able to dethrone the original Avengers at the US box office this weekend, opening to a huge $187 million weekend but still falling short of the $207 million opening of its predecessor, according to Box Office Mojo. Ultron was forecasted to come in ahead of the original Avengers, which would have meant taking over the title of all-time biggest opener and making suits at Marvel and Disney very, very happy. They certainly still have little to complain about — Ultron also brought in $439 million internationally and is yet to open in Japan or China — but it's also a sign, however slight, that Marvel's power has its limits.

There's no definitive answer to why Ultron fell behind the original Avengers, but there are plenty of possibilities that you can point to. Variety suggests that the wealth of sports events this weekend, including the Kentucky Derby and the Mayweather–Pacquiao fight, gave potential viewers a lot of other options. "It was one of greatest sports days perhaps in history," Dave Hollis, Disney's distribution chief, tells Variety. "It feels like the barrage of sporting options grabbed a lot of people’s attention."

The other potential factor is some mix of superhero fatigue and Ultron's cooler reception. Ultron's reviews weren't quite as glowing as the reviews for Marvel's first Avengers. And the fact is that Ultron isn't quite as special: this is the second time Marvel has gotten its ensemble of stars together for a film, and we now know that it's going to happen again and again and again. That's true for movies outside of the Marvel universe as well. We're about to get huge ensemble films from DC Comics, and basically every franchise in existence is about to launch a connected world.

For now, Marvel still doesn't have much cause for concern. Ultron's opening, though a minor disappointment, is still a huge success. Marvel now has the three biggest US openings of all time, with Iron Man 3 taking third place with its $174 million opening in 2013. The Hollywood Reporter has some interesting statistics about who went out to see Ultron, suggesting that Marvel is already reaching a wide audience. Men made up 59 percent of viewers, and about 60 percent of viewers were 25 or older.