“Two Mules for Sister Sara” : Shirley MacLaine and Clint Eastwood are opposites in politics, but have an amazing collaboration.

OU MIGHT be surprised to see Shirley MacLaine’s name listed first in the credits of a Clint Eastwood Western directed by Don Siegel. In his commentary, filmmaker Alex Cox (“Repo Man,” “Sid and Nancy”) says there were two reasons. It was the “gentlemanly” thing to do and it reflected MacLaine’s considerable star power.

She’d already received Best Actress Oscar nominations for “Some Came Running” and Billy Wilder’s “The Apartment” and “Irma la Douce.” After bit parts in “Revenge of the Creature” and “Tarantula” and starring on TV’s “Rawhide,” he cemented his bona fides in Sergio Leone’s iconic Man With No Name trilogy – “A Fistful of Dollars,” “For a Few Dollars More ,” “The Good, the Bad and the Ugly.”

That they were polar opposites on the political spectrum didn’t matter: Their chemistry was undeniable.Good thing, too. In an interview from his Carmel, CA, home, Eastwood says that he and MacLaine share the screen for 75 percent of the running time, which played to Siegel’s mastery of pacing and timing. “Two Mules for Sister Sara” doesn’t hurt for all-out action – a railroad bridge is dynamized and a French garrison attacked, for starters – but it’s all driven by Eastwood and MacLaine.

Well, them and a crew of other stars.Siegel, who would partner with Eastwood the next year on “The Beguiled” and “Dirty Harry” (their first project was 1968’s “Coogan’s Bluff”) had the original “Invasion of the Body Snatchers” ” and “The Killers” under his belt.” Albert Waltz (an Oscar nominee for “Pride of the Marines” and “Broken Arrow”) wrote the script from a story by Budd Boetticher (ditto, “Bullfighter and the Lady”). The cinematographer was Gabriel Figueroa (ditto-ditto, “The Night of the Iguana”) and the composer was the inimitable Ennio Morricone.

Cox, also the author of “10,000 Ways to Die: A Director’s Take on the Italian Western,” points out that “Two Mules” was Siegel’s first foray into Mexico. It had become a go-to shooting location thanks to Sam Peckinpah (“The Wild Bunch”), John Wayne (“The War Wagon”) and other filmmakers, but Siegel steered clear of familiar locales, which also set this Western apart.

Hogan, a gruff, shoot-first loner, isn’t exactly lifted from Eastwood’s 1970 playbook, either.He’s bringing dynamite to the Mexicans for their attack on the occupying French – his cause is the outpost strongbox, not independence – when he comes across some bandits about to assault the good sister (MacLaine). After he, naturally, guns them down there’s, naturally, no way they’ll split up. Sara’s wanted by the French for aiding the Mexicans, and as Hogan begins to suspect that she isn’t who she says she is, their relationship – he’s confounded and frustrated, she’s enigmatic and single-minded – develops along unexpected, often laugh-out -loud lines. It’s great fun watching them work it.

Still not convinced? Hogan has to lean on Sara big-time following a run-in with a band of Yaquis, and still isn’t 100 percent when they go down to the wire to bring down a train. The results are spectacular, but he could never have pulled it off alone.