It’s only in retrospect that we recognize the watershed films, the ones that signaled the end of one era and the beginning of another.

Michael Mann’s feature film debut “Thief” earned decent enough reviews when it was released in March of 1981. The New York Times and Washington Post didn’t “get” it. Chicago homers Siskel and Ebert praised the Chicago-shot thriller to the heavens, which is what they did for most movies made in Chicago. And the film sold just enough tickets to cover its budget.

But seeing it now, it’s easy to appreciate the shimmer Mann brought in to replace ’70s grit — wet, lurid, neon-washed streets, shiny semiautomatic pistols, good haircuts, pricey cars and sleek fashions.

There’s a lot here — style over “details, Mann’s “MTV Cops” pitch that became “Miami Vice,” Chicago cop Dennis Farina, who’d go greyer, get a haircut and move to 1960s Vegas for “Crime Story,” the hardened, bullying criminal/star who’d put a premium on professionalism (“Heat,” “Collateral”).

“Thief” is a James Caan star vehicle, one of his very best. Unleashing the trim and muscular Caan as an unlikeable, bullying lead, pairing him with Tuesday Weld, making the very young Chicagoan Jim Belushi a sidekick and Willie Nelson a convict/mentor, giving Robert Prosky his best pre-“Hill Street Blues” boost, so many elements of this striking and lean classic seem obvious that one forgets how inspired those casting, plot and design touches turned out to be.

Mann loosely adapted a cat burglar’s memoir into a “one last score” genre thriller of an ex-con who owns a used car dealership by day, cracks safes by night. Frank is all business while on the job, and when something goes wrong with “my cut.”

But he’d like “the life” — a wife, kids, suburban comfort. So this hostess (Weld) at a diner where he makes his “stones” transactions (selling stolen diamonds to middle men) is who he asks “We goin’ out tonight?” He’s very late showing up, but he bullies her and anybody in the blues club where they meet into going through the with evening.

“I have run out of time. I have lost it all. So I can’t work fast enough to catch up. I can’t run fast enough to catch up. And the only thing that catches me up is doing my magic act.”

She doesn’t blanch when he flashes his pistol at a bystander, which tells us something. Maybe she’ll go along with what amounts to a brusque and blunt proposal over coffee as Frank “cards on the tables” her like a man who knows a woman who’d “get” him in an instant.

“What the hell do you think I do?…I wear $150 slacks, I wear silk shirts, I wear $800 suits, I wear a gold watch, I wear a perfect, D-flawless three carat ring. I change cars like other guys change their f—–g shoes. I’m a thief. I’ve been in prison, all right?

Frank has a lot, but he needs more. He promises to get his cellmate/mentor (Nelson) out of prison. Jessie (Weld) blurts out she can’t have kids, and ex-cons can’t adopt. Not easily, anyway.

He needs that big score to set him up. And there’s this grandfatherly old hoodlum (Prosky) he meets when somebody tries to steal some of his stolen loot who assures him he can solve his all of his problems, “like family.”

There’s just this one impossible job old Leo would like Frank to do…

“Thief” is as tight and streamlined as two hour and nine minute movies get. Every scene feels compact, driven by the wound-up watchspring that is Caan at his most engaged.

The courtship scene and the confrontations are punched through, the nuts and bolts of breaking and entering, cracking a safe, leaning on a blue collar metalurgy ex-con expert to figure out how to cut through “Swedish rolled steel” leave little out and contain no extraneous information.

The math of Frank’s Joliet prison years and the fact that he’s got a Caddy/Buick/used Yank tank dealership after being out only four years is a mystery. And how does one learn 1980s safe-cracking from a 1950s vintage old-timer in prison?

Momentum is what matters — a look, a feel, a stylish underworld-guy-in-a-hurry vibe. Cinematographer Donald Thorin would go on to film “Tango & Cash,” the ’80s at their slickest and most vapid. Production designer Mel Bourne would help romanticize “The Natural.”

Whatever other work “Thief” inspired in style, script and design, the movie that kept coming to my mind repeatedly throughout it is “Straight Time,” Dustin Hoffman’s lean, downbeat and gritty ex-con thriller from 1978. The films are similarly set, equally violent and equally involving and yet whole eras apart, despite being separated by just three years.

“Straight Time” is a fin de siecle ’70s crime thriller, the logical conclusion to the era “The French Connection,” “The Getaway” and “The Taking of Pelham 123” kicked off.

“Thief” was something new, shedding some of the grit to get in more visual sizzle.

Luc Besson and generations of thriller filmmakers who followed took their cue from Michael Mann’s debut — park tough but always “professional” criminals in an underworld that’s more sexy than seedy. Dress them up a bit. And let it be and damp only after dark. Because that’s when the gunshots flash and when the blurred neon in the rain puddles is most striking.

Rating: R, violence, profanity

Cast: James Caan, Tuesday Weld, Jim Belushi, Willie Nelson, Tom Signorelli, Dennis Farina and Robert Prosky.

Credits: Scripted and directed by Michael Mann, based on the memoir of Frank Hohimer, “The Home Invaders: Confessions of a Cat Burglar.”

Running time: 2:09