In a perfect playing field, the weekend’s head-on showdown between “Thor” and “Fast Five” would have never happened — but it did, thanks to a wild reshuffling many months ago that had studios chasing each other all over the summer calendar.

It all started with “Thor”: Paramount originally had flirted with several dates before settling on May 20 to launch its latest comicbook tentpole. But when Disney claimed that weekend for “Pirates of the Caribbean: On Stranger Tides,” Par moved up “Thor” to May 6, trading a Memorial Day-lead in for its eventual summer kickoff slot.

Fast forward more than 10 months, and a good while after Universal announced its June 10 release date for “Fast Five,” Par slotted “Super 8” to bow the same weekend as U’s newest “Fast and Furious” installment. In response, U then decided to bump up “Fast Five” to bow on April 29, just a week before “Thor’s” Stateside kickoff.

Like a highly strategic chess game, distributors are constantly jockeying for the best possible launch dates. And in the case of this past weekend’s tentpole gridlock, “Fast Five” was coming off what essentially had been the jump-start to the summer season with a boffo $86 million domestic opening, while “Thor” looked to nab its share of summer-ready filmgoers.

Both films still managed sizeable openings, while “Fast Five” even scored a typical — though not desirable — soph-sesh drop of 62%.

The weekend’s “Thor”-“Fast Five” collision had the biggest impact at Imax locations, a vast majority of which swept out “Five” to make way for the God of Thunder. Since both pics had been committed to their Imax positions before swapping dates, Universal knew ahead of time what it was getting into, choosing the second-week Imax plunge over a head-to-head tussle with “Super 8.”

“We committed ourselves to being the first summer blockbuster this year,” said U distribution prez Nikki Rocco. “But we also went in with our eyes wide open, knowing that Imax had already committed to ‘Thor.'”

Last weekend, Imax repped nine of “Fast Five’s” top ten theaters, with the film at a total 243 debut Imax locations. That figure dropped this weekend to 32 film-based runs, while “Thor” occupied 214 digital-only Imax engagements. Imax has a similar back-to-back lineup with “Cars 2” on June 24, followed a week later by “Transformers: Dark of the Moon” on July 1.

But regardless of a film’s format, bizzers should brace themselves for more battles like this past weekend’s, as tentpoles stockpiling the sked has become this summer’s reality.