Here’s a recommendation I never thought I’d issue as a film critic: Consider watching just the first half of the overachievement-gone-awry biopic “Molly’s Game.” The initial hour of Aaron Sorkin’s directorial debut is fizzy, smart, exhilarating fun; it would’ve made a fantastically promising TV pilot.

“Molly’s Game” opens with a sensational skiing segment, at the bone-crunching end of which tiger-fathered Molly Bloom (Jessica Chastain), then an Olympic hopeful, has to become the best at something not sports-related. Putting off law school, Molly stumbles into the poker underworld, where, for a little while at least, she becomes the biggest game runner in the world.

Written by Sorkin, this adaptation of Bloom’s memoir is loquacious in the extreme, with the fictionalized Molly explaining something about poker, the law, her life, and the FBI’s case against her via voiceover in practically every scene. For a long while — much longer than I would have thought — I didn’t mind.

Watch Video: Jessica Chastain Is the 'Poker Princess' in Aaron Sorkin's 'Molly's Game' Trailer

Chastain brings an intoxicating swagger and a poignant injuredness to her poker-hostess-turned-eventual-felon as a woman who knows she could succeed at anything, and decides to enter the male-only caves where powerful millionaires win or lose the equivalent of an upper-middle-class annual income in a single night. Molly’s ascent is canny and swift. Her downfalls (she suffers several) are sudden and inevitable.

It’s not just that underdog stories — in this case, of a female poker organizer — tend to be more exciting than the hangovers thereafter. In its first half, “Molly’s Game” immerses its viewers in both the rush of the bet and the thrill of how power works in a boys’ club. (Expect jargon like “calling on the flop” and “bombing the river.”)

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She quickly absorbs everything she needs to know from an abusive boss (Jeremy Strong) and sets up shop for herself, learning along the way how to look the part of a woman who can command a $10,000 admission fee to her poker nights. The costuming and makeup tell stories of their own, as Molly morphs from a JCPenney shopper to a “Cinemax version of herself.”

But Molly doesn’t quite grasp the precariousness of her position by dint of her gender until it’s too late. And when she thinks she’s finally grasped how sexism can knock her down, she’s forced to learn the same lesson even more ruefully the next time.

If anyone ever needed a (platonic) girlfriend, it’s Molly. In this telling, at least, the game runner is lonely and often on the verge of depression, driven by a need to succeed — not just admirably, but wildly and wondrously. Always, she is surrounded by men. In the present, her lawyer (Idris Elba in an utterly thankless role) slowly realizes how nobly principled she is despite her chosen profession of encouraging gambling addiction, a requirement of the job she regrets.

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In flashbacks and during her legal troubles, her hard-nosed father (Kevin Costner) offers some tough love. Her celebrity draw in LA, a poker luminary rumored to be based on Tobey Maguire (played by a surprisingly sexy Michael Cera), eventually reveals his predatory ruthlessness. Another client (a hilarious Chris O’Dowd), an unreliable drunk in New York with a penchant for Dadaist mumblings, inadvertently robs Molly of her extraordinary good luck.

It’s clear from the first few minutes of the film that Molly has the potential to climb to the top of any mountain she chose, so why did she pick poker? The desperately flawed second half of “Molly’s Game” searches for an answer, and the explanation, elaborated in a pivotal scene between Molly and her father, is so crude, simplistic, and tone-deaf that it threatens to torpedo the picture.

That may sound like an exaggeration, but it’s not. It’s an atrocious scene that demeaningly recasts Molly’s accomplishments as a juvenile rebellion, with Costner’s psychologist father shrinksplaining to his daughter why she is the way she is despite her protestations otherwise. (Of course, we’re supposed to trust that it’s the dad, not Molly herself, who’s right about what drives her.) Viewers of the Sorkin-penned “Steve Jobs” might recall that that biopic, too, hinged on some piffling psychoanalysis to patch things up between an estranged father and daughter.

The second, fatal blow — the Fat Man to the above scene’s Little Boy — comes courtesy of the absolutely ludicrous final courtroom scene, in which pompous self-righteousness carries the day. It’s too bad that Chastain’s heady, exquisitely subtle performance is dragged down by the  laughably vehement male characters that seek to speak for her.

You can’t keep a good woman down. But you can constantly talk over her, I guess.