A fourth Shrek movie unfortunately seems unavoidable, given that “Shrek The Third” took in an estimated $122 during its first three days in theaters. That’s the best-ever opening for an animated picture, smashing the record held by the second “Shrek,” and the No. 3 opening of any type of film of all time, following “Spider-Man 3” and “Pirates of the Caribbean: Dead Man’s Chest.” It’s also the best-ever opening for Paramount Pictures, proud owners of DreamWorks Pictures, which released the first two “Shrek” pictures on its own. Just what a good investment Paramount made is underlined by the fact the take of Shrek’s first three days is approximately equal to the combined opening-weekend take of Paramount’s previous No. 1 and No. openers, “War of the Worlds” and “Mission: Impossible 2.” Both of which, of course, starred the studio’s former longtime box-office king, Tom Cruise. “Shrek The Third” sold something like two-third of all tickets in North America this weekend, helped no doubt by the absence of a single other new wide release, a brief 81-minute running time — and a 50 percent drop for “Spider-Man 3,” which still managed $28 million and has grossed $281 million so far in North America alone. Interestingly, “Shrek the Third” just missed out scoring the weekend’s best per-theater average. That mark is apparently held by Fox Searchlight’s well-reviewed Irish musical “Once,” which scored an astounding $30,256 per venue average at two locations, vs. $29,597 for “Shrek the Third” at a whopping 4122 (and an estimated 10,000-plus screens). The reign of “Shrek the Third” at No. 1 will, of course, be brief. “Pirates of the Carribean: At World’s End” docks at a massive number of theaters Thursday night at 8 p.m., and is expected to give “Spidey 3” a run for the all-time opening title, even with a shiver-me-timbers running time of 167 minutes.