Stateside summer box office got off to an early start last weekend with Universal’s boffo $86 million opening for “Fast Five.” Now, Paramount looks to turn that momentum to its favor with Marvel 3D tentpole “Thor” kicking off its domestic run at 3,955 locations, of which 2,737 will be in 3D and 214 in Imax.

“Thor” already has cumed $108.4 million internationally through Monday, thanks to last week’s early offshore bow in nearly every major market outside the U.S. Current worldwide tally for “Fast Five” stands at $185.8 million.

The start of the summer B.O. sesh has expanded in recent years to the first weekend in May, but last weekend’s “Fast Five” essentially moved that launch even earand “Fast Five” kickstarted their runs overseas before bowing domestically.

Still, most B.O. pundits agree that “Fast Five” has helped kickstart moviegoers’ appetites for summer’s tentpoles, which bodes well for “Thor” this weekend.

The comicbook adaptation, budgeted at a reported $150 million, is expected to open to $55 million Stateside, according to Par. But rival studios said the film is more likely to gross north of $60 million, based on pre-weekend tracking. Pic faces holdover competition in “Fast Five,” which in its second frame will likely continue to draw a sizable share of male auds — “Thor’s” core demographic. “Fast Five,” which has cumed $103.2 million domestically through Wednesday, may see a better-than-average hold ranging from 45%-50%.

The weekend’s female-driven counterprogramming, Warner Bros.’ “Something Borrowed” and Sony’s “Jumping the Broom,” aren’t expected to set the frame ablaze, though expected low-teens or high single-digits launches for either film would be a solid start for the modestly budgeted pair. Warners launches “Something Borrowed” today at 2,904 locations; “Jumping the Broom,” from Sony’s TriStar banner, debuts at 2,035.

Summit’s Jodie Foster-helmed “The Beaver,” toplining Mel Gibson and Foster, bows this weekend in the top 10 U.S. markets at 22 engagements. Summit plans to expand the film May 20 weekend.

Also in limited release, but considerably wider than “The Beaver,” helmer Roland Joffe’s latest historical drama “There Be Dragons” kicks off its Stateside launch today at 259 locations via distrib Samuel Goldwyn.

This time last year, Paramount dominated the U.S. box office with another Marvel comicbook tentpole, “Iron Man 2,” which opened to $128 million. Par also went a week early internationally with “Iron Man 2,” hoping to add a week of overseas play before Universal launched “Robin Hood.” Par employed a similar release strategy with “Thor” in light of Disney’s global debut of “Pirates of the Caribbean: On Stranger Tides” on May 20.

And while “Thor” isn’t expected to reach “Iron Man’s” debut mark, the combined weekend takes of both “Thor” and “Fast Five” could keep overall box office totals in step with the same frame last year.

“Thor” is tracking best with males audiences over 25, followed by under-25 men and teens, all of which could mean better business in 3D and Imax. Pic has OK tracking with families.

With “Something Borrowed,” Warners expects to attract predominately female filmgoers who aren’t buying tickets for “Thor,” while “Jumping the Broom” should see a strong contingent of ethnic women. “Something Borrowed” cost a reported $30 million; “Jumping the Broom” came in just under $7 million after tax rebates and location incentives.

Both femme-driven new entries should see solid mid-week figures as those pics generally play well to women during the week.

The weekend’s most notable holdovers, led by 20th Century Fox’s “Rio,” will also help boost weekend totals. “Rio” has held nicely in repeat frames, down 45% last weekend, with a Stateside cume of $106 million. Lionsgate’s “Tyler Perry’s Madea’s Big Happy Family” and Fox’s “Water for Elephants,” both entering their third frames, have tallied $42.5 million and $35.2 million, respectively.