“American Assassin” is a Big Action Beats formula thriller that overstays its welcome and never quite gels around its hunky young star, allowing Michael Keaton to steal the movie out from under him.

Just like “Spider-Man,” in other words.

It makes the most of what is a supremely silly premise — that a young man, grievously wounded in the terrorist attack that killed the woman he’d just asked to marry him — can have his revenge on his own terms thanks to self-help training he devises himself. And that the CIA would nab him, letting him skip from Ibiza to Warsaw, Istanbul to Rome, hurling this largely self-trained “assassin” at terrorists like the ones who did in that lovely fiance.

Dylan O’Brien of “The Maze Runner” and TV’s “Teen Wolf” is Mitch Rapp, just an ordinary American rule-breaker/rogue who channels his rage about the murder of his beloved into mixed martial arts training, practice-range precision and commitment to learn both Islam and Arabic.

Which he needs to pass the online “So you want to be a jihadi” quiz that the group he wants to infiltrate, the cell that carried out the mass murder on a Spanish beach, uses to test him.

“I want to bathe my hands in the Blood of Infidels!”

We’ve got a winner!

But his web presence has attracted the CIA’s attention, in the persons of functionaries played by Sanaa Lathan and David Suchet. And after some back-and-forth, Mitch goes into the program of the baddest of the Agency’s baddasses — Hurley, played with all the demonic glee the revived Michael Keaton can give him.

Keaton’s best scenes are the training sequences cooked up by director Michael Cuesta and the five credited writers who adapted Vince Flynn’s boilerplate terrorist-killer novel. Hand-to-hand combat drills, VR pick-out-terror-target practices, all manner of think-fast scenarios are hurled by Hurley at his Orion team. He likes shooting a pistol over their heads in mid-practice.

“You flinch, you die.”

They have to be ready because “The enemy dresses like a deer and kills like a lion!”

The mission they’re prepping for involves the usual missing Russian plutonium, a nuclear bomb headed into the wrong hands and the Hurley apprentice (Taylor Kitsch) gone rogue and helping the bad guys.

All standard-issue James Bond  plot points, circa 1989, with requisite chases, brawls and exotic settings.

But director Cuesta (“Kill the Messenger”) and his not-inhumanly beefed-up leading man do well with the many fights. The kid loses his shirt often enough for us to stop staring at the sexy agent (Shiva Negar) assigned to the mission. Almost.

But he’s stuck playing an worn-out archetype — a rebel with a cause, and a way with firearms and knives.

Cuesta shows his true focus early and often, and in the most obvious way the movies have of doing that. He gives Keaton close-up after close-up, almost ALL the close-ups — which throws the whole enterprise off balance. And Keaton knows what to do when the camera is that tight — chew that scenery and spit it out.

But if this is a potential “franchise,” it’s not going to be built around him — fit as he may be, he is newly-turned 66.

“Franchise” comes down to “the kid.” And O’Brien, even if he has the physical skills and a way with his flintiest lines — “My goal is to have them awake at night, knowing I’m coming for them.” — doesn’t pop off the screen, not in this star-vehicle at least, not for two hours worth of generic nuclear terror thriller.

MPAA Rating: R, for Strong violence throughout, some torture, language and brief nudity.

Cast: Dylan O’Brien, Michael Keaton, Taylor Kitsch, Sanaa Lathan, Shiva Negar, David Suchet

Credits: Directed by Michael Cuesta, script by Stephen Schiff, Michael Finch, Edward Zwick and Marshall Herskovitz, based on the Vince Flynn novel. A Lionsgate/CBS release.

Running time: 1:51