Summer has officially arrived at the domestic B.O., as Paramount and Marvel Entertainment’s “Iron Man 2” debuted with an estimated $133.6 million at 4,380 engagements — without the crutch of higher 3D ticket prices.

The 2D comicbook sequel, which now ranks as Par’s highest-grossing domestic opener, took in an additional $57.2 million in 61 overseas markets on 10,774 screens over the weekend boosting its worldwide haul to a stellar $327.6 million. The film bowed internationally last weekend in 53 territories, kickstarting the season first overseas due to World Cup dates.

The decision led up to a successful domestic bow as “Iron Man 2” became the fifth-highest three-day opener ever domestically, surpassing “Shrek the Third,” which debuted with $121.6 million in 2007.

Focus Features’ Mother’s Day-positioned docu “Babies” opened with a solid estimate of $1.6 million at 534 locations. The docu scored a per-screen average of $2,951.

The robust openings helped boost the frame by approximately 18% over the comparable period last year, which saw Par’s “Star Trek” bow to $79.2 mil lion. Like “Star Trek,” “Iron Man 2” reps a significant debut for Par given that the 2D film was unable to benefit from 3D upcharges.

Still, Par vice chair Rob Moore admitted the 3D component has become a primary focus for major releases. The studio will launch Marvel’s “Thor” during the same weekend next year but was tightlipped on whether the film will get the 3D treatment.

” ‘Iron Man 2″ is “really the last big movie that was still shooting before the 3D context of ‘Avatar’ and ‘Alice in Wonderland,'” Moore said. “So while 3D wasn’t a huge part of the conversation, going forward every tentpole for next summer will have that evaluation.”

“Iron Man 2” still managed to outperform the 3D “Avatar” in opening Imax grosses. At 181 Imax locations, pic boasted a record-breaking take of $10.2 million, some $700,000 more than “Avatar.” Imax share repped 8% of “Iron Man 2’s” total weekend gross on the same percentage of engagements.

Driven primarily by male auds, with a 60%-40% male-female split, “Iron Man 2” outpaced the original, which debuted in 2008 with $102.1 million; domestic cume was $318.4 million.

“Iron Man 2” is Marvel’s first release since its pact with Disney.

Moore admitted that the Iron Man property has a smaller fanbase than either Batman or Spider-Man. The most recent installments in those franchises, “The Dark Knight” and “Spider-Man 3,” rep the top three-day record holders, with $158.4 million and $151.1 million, respectively.

“To be in that group of some of the biggest openings of all time really is a testament to the movie (director) Jon Favreau has created and the character that Robert Downey Jr. has personified,” Moore added.

Downey now boasts four consecutive commercial hits, with “Iron Man,” Warner Bros.’ “Sherlock Holmes” and Par and DreamWorks’ laffer “Tropic Thunder.” “Sherlock Holmes” was one of last year’s holiday hits, grossing $209 million domestically, while “Tropic Thunder” took in $110.5 million Stateside.

Rated PG-13, “Iron Man 2” scored an overall A CinemaScore rating, which could draw repeat business among its core aud in subsequent frames. Franchise enthusiasts drove Friday’s $52.3 million take, including $7.5 million in midnight grosses. Pic dropped 11% on Saturday, with $46.5 million.

Par estimated moderate earnings on Sunday, when even fanboys were likely busy brunching with mom. However, last year, “Star Trek” earned $2 million more than what Par had projected for Mother’s Day.

The frame’s holdover crop was led by Warner’s horror pic “A Nightmare on Elm Street,” down a sizable 71% in its soph sesh, for an estimated weekend take of $9.2 million. “Nightmare” fell to the No. 2 spot after topping the chart last weekend with $32.9 million; pic’s cume stands at an estimated $48.5 million.

Entering its seventh frame, Par’s 3D toon continues to hold well, with an estimated $6.8 million at 3,003 locations, down 36% from last weekend. Also showing strong holdover potential is 20th Century Fox’s romantic comedy “Date Night,” which fell only 30% in its fifth frame for an estimated gross of $5.3 million at 2,734. “Dragon” surpassed the $200 million mark this weekend, while “Date Night” has cumed an outstanding $80.8 million.

Movies with mamas

Focus hopes it tempted mothers on Sunday after its focused marketing campaign for “Babies.” Distrib’s prexy of theatrical distribution Jack Foley said the docu performed best at arthouse theaters.

“Babies” saw an 80% uptick from Friday to Saturday, which Foley said he hoped would translate to Sunday.

Sony Pictures Classics debuted Rodrigo Garcia’s “Mother and Child,” with an estimated $44,488 at four locations in New York and L.A. Pic toplines Annette Bening and Naomi Watts as an estranged mother-daughter duo, with Kerry Washington portraying a woman who wants to adopt.

Pic’s maternal theme may have tempted specialty auds on Mother’s Day, with SPC estimating a solid per-screen average of $11,122.

Distrib also expanded Nicole Holofcener’s “Please Give,” starring Catherine Keener and Oliver Platt, to 26 locations, up 21 from last weekend. The dramedy earned an estimated $253,135 for a per-screen average of $9,736.

China’s ‘Iron’ ore

On the international front, China ranked as the top territory for “Iron Man 2,” debuting with an estimated $7.3 million at approximately 3,000 locations. In Germany, the sequel opened 15% ahead of its predecessor with an estimated $3.3 million; Concorde is distribbing in that territory.

“Iron Man 2” opened last weekend in 53 markets and added eight to its overseas roster in the film’s second frame.

Among the film’s notable holdover territories, the U.K. led the barrage, grossing an estimated $4.9 million for a drop of 53%. South Korea followed, down 57%, with a weekend estimate of $4.7 million. Respective cumes for the territories stand at $23 million and $22 million.

Disney’s 3D fantasy “Alice in Wonderland” held best against the “Iron” onslaught, totaling an estimated $12.5 million on 5,946 screens in 54 territories. In its 10th week of play overseas, the film continues its steady march toward $1 billion worldwide. International totals reached $629.5 million, boosting its worldwide figure to $960.3 million.

Top territory for “Alice” was Japan, where the film claimed the top spot for its fourth consecutive week. Japanese auds shelled out $5 million, bringing cume to an estimated $89 million in that territory.

Meanwhile, Warner debuted “Nightmare” in 10 international markets, estimating $6.7 million on more than 1,200 screens. Pic outranked the soph sesh of “Iron Man 2” in Russia, where the horror pic bowed to an estimated $3.2 million on 525.

“Nightmare” debuted in Blighty, claiming the territory’s No. 2 spot with an estimated $2.2 million on 354. Pic is set to launch in France and Mexico next weekend, followed by Germany, South Korea and Australia on May 20.