King of the keg-stand this weekend, Universal’s R-rated frat comedy “Neighbors,” with its estimated boffo $51.1 million opening, interrupted the Stateside reign of “The Amazing Spider-Man 2,” which fell a steeper-than-expected 59% in its second frame for a projected $37.2 million through Sunday.

The Sony superhero tentpole — which did, however, hold onto the overseas weekend crown, with its estimated $69.5 million — reached a total $550 million worldwide, of which more than $400 million comes from international markets.

“Ultimately, (the domestic drop) was within the realm of a picture of this size,” said Sony worldwide distribution chief Rory Bruer.

That said, “Spider-Man” suffered from the mega-buzz building around “Neighbors” for the past several weeks. The Seth Rogen-Zac Efron comedy ultimately played best with women, at 53%, though men accounted for a respectable 47% of the opening.

Universal prexy of domestic distribution Nikki Rocco said she is estimating a 30% drop from Friday to Sunday, but that could be better given the film’s strong playability with women.

“I never thought this would be a choice on Mom’s Day,” Rocco admitted.

Though uncertain, the $18 million-budgeted film’s cumulative heights are expected to be stellar regardless. “Neighbors” overperformed much like “Ted” did last year, when it beat its mid-to-high $30 million expectations with a $54 million domestic opening.

Universal also bowed “Neighbors” in 29 international territories, where it overperformed with $34.4 million. Not surprisingly, the pic’s largest-grossing markets were the U.K., which contributed $14.7 million, and Australia, with $7.1 million.

Elsewhere in the Unites States, Sony bowed femme-targeted “Mom’s Night Out” — the $5 million-budgeted family comedy from TriStar — at 1,044 locations, grossing an estimated $4.2 million. The distrib is projecting an 11% uptick for the pic on Mother’s Day.

Clarius Entertainment (via Freestyle Releasing) bowed animated kidpic “Legends of Oz: Dorothy’s Return” at an aggressive 2,607 theaters, though the film estimated just $3.7 million in three days. The toon is one of only a few films this summer aimed at young kids; its domestic prospects are unlikely to grow, however.

In limited release, Open Road launched Jon Favreau’s food comedy “Chef” at six engagements, averaging a standout $34,034 per screen, with a total estimated $204,201 through Sunday. The film should leg out nicely given that 93% of the film’s exit scores were the highest-two ratings, according to the distrib.