“Arthur the King” is a sweetly sentimental story all but guaranteed to move any dog fancier to tears.

A Mark Wahlberg star vehicle in which he’s more or less second banana to a dog — at least when they’re on screen together — it balances some gripping action with canine melodrama, teaching us as it does about the extreme sport this “true story” is set against — team Adventure Racing.

Wahlberg plays a headstrong star in the three-men/one-woman team sport that sees competitors run, climb, bike and kayak across hundreds of miles of some of the world’s most impassible wild terrain. But as “all-in” as Mike Light is, he’s never brought home the top prize.

When we meet him, he’s bullheaded a team into paddling in defiance of the tide and losing one last time, ignoring the solid advice and protests of the more media savvy teammate, Leo (Simu Liu of “Shang Chi and the Legend of the Ten Rings” and “Barbie”), who shames him with a viral video.

Three years later, Mike’s not-quite-resigned to helping run his Dad’s (Paul Guilfoyle) Colorado real estate business and raising his little girl with his retired-competitor wife Helena (Juliet Rylance). But Mike wants that “one last shot.”

“Racers race. This is not how it ends for me.”

We see him round up an under-tested (Nathalie Emmanuel) climber/competitor, a canny but older “bum knee” navigator/veteran like himself (Ali Suliman) and reluctant sponsors for a team leader who never comes out on top.

Social media star Leo is the only way they land the money, setting up an in-team rivalry as we wonder if Mike will screw it up again, or learn to be a “team” player.

That could very well be the case as they struggle during the early stages of a 400-mile+ dash over, through and around the Dominican Republic for a world championship.

But we’ve also been following the plight of a street dog of Santo Domingo, an injured mutt who’s been abused and tested by this life on his own.

“Arthur the King” is the name he’s given when he shows up, mid-race, to aid and inspire the team.

The Michael Brandt script and director Simon Cellan Jones, who directed Wahlberg’s “The Family Plan” fictionalize the tale — a Swede named Mikael Lindnord was the one who met Arthur, and wrote a book about him — and ensure that the first two thirds of the movie are overwhelmingly devoted to assembling the team and the “embrace pain, buckets of it” nature of the race, where “suffering is a skill” one and all must master.

The scenery is spectacular. The players do a decent job of getting across the superhuman efforts required and the stunt crew delivers one doozy — involving mountain bikes, a “short cut” and a zipline.

But the picture doesn’t find its stakes until this bloodied dog joins them in their quest.

The script tries and fails to find a “villain” for the tale, something a few “true story” films struggle with. A trash talking Aussie (Rob Collins) is the best they could manage. The snarky, funny Liu would have better served that purpose, but what can you do?

The Hollywood focus on Wahlberg’s Americanized character distracts us from the actions of the dog, which seem pretty far-fetched on the surface.

But if we focus on the dog and his struggles, we have to try not to pretend there’s anything off-putting in these entitled fringe-sport athletes competing in some of the poorest places on Earth for their races, where emaciated dogs are but one sign of the poverty of their vacation destination.

I found myself focusing on how the athletic star Wahlberg related to the dog (played by a team of matched canines), how the instant empathy his character is scripted as having seems harder to play than the acceptance of their mascot in later scenes.

But as manipulative as this has to be, as far-fetched as some of the story plays, the film’s heartwarming virtues cannot be denied. The dog training — thank GOD they used real dogs and not digital ones — paid off, and Arthur shows a little bit of personality, mostly in the eyes.

And if you don’t get a little choked up by the finale, you may find yourself condemned to watching “My Dog Skip,” “Marley & Me” and “A Dog’s Purpose” in Purgatory until you get the message.

Rating: PG-13, profanity

Cast: Mark Wahlberg, Nathalie Emmanuel, Simu Liu, Juliet Rylance, Paul Guilfoyle, Rob Collins and Ali Suliman.

Credits: Directed by Simon Cellan Jones, scripted by Michael Brandt, based on the book by Mikael Lindnord. A Lionsgate release.

Running time: 1:30