Holding the 19th pick Thursday night, the Dallas Cowboys watched the first half of the NFL Draft’s first round unfold in ideal fashion. They needed a wide receiver, having just cut longtime cornerstone Dez Bryant and possessing no real No. 1 replacement, despite their free agency addition of Allen Hurns. No team had taken a wideout in front of them, giving them the chance to choose any they wanted. It seemed perfect for Dallas, and seemed obvious what would happen next.

And then came the Cowboys’ choice: Leighton Vander Esch, a linebacker out of Boise State.

The NFL moves in cycles, and one takeaway from Thursday night is that the perceived value of wide receivers in the draft is on a downward trajectory, most likely for good reason. Teams selected only two wide receivers in the first round, the lowest total since 2010. No wideouts came off the board until the Carolina Panthers took Maryland’s D.J. Moore 24th, the latest the first wide receiver was taken since 2008, when none went in the first round.

That 2008 draft turned out to be aberrational — six wideouts went in the 2009 first round, including two in the top 10. This year, though, feels like it may be the start of a trend. For years, running backs were disparaged as interchangeable and unworthy of high picks. It’s possible wide receivers are about to take a turn as the new running backs.

In recent seasons, teams choosing wideouts early have rarely reaped a benefit, while some of the NFL’s best wideouts emerged in later rounds. Last year, three wideouts went in the top 10. Corey Davis, the fifth pick, led them with 34 catches for 375 yards, and John Ross, the ninth pick, didn’t catch a single pass. Meanwhile, JuJu Smith-Schuster and Cooper Kupp — the 62nd and 69th overall picks — contributed heavily to playoff teams as secondary options.

Over the six first rounds before Thursday night, NFL teams selected 25 wide receivers in the first round. The 2014 draft was a bonanza, producing a first round with Odell Beckham Jr., Mike Evans, Sammy Watkins and Brandin Cooks. The year before, the Texans took DeAndre Hopkins late in the first round. The Raiders probably do not have much regret taking Amari Cooper fourth overall in 2015, even after a down year last season. The remaining list of 19 wide receivers is a mix of flat-out misses and players yet to fulfill potential.

Meanwhile, stars such as T.Y. Hilton (third round), Stefon Diggs (fifth), Keenan Allen (third) and Alshon Jeffery (second) were picked after the first round. Antonio Brown, the best wide receiver in the league, was a sixth-round pick. It’s cherry-picking to say teams can find quality receivers in any round; that’s true of any position. But trying to discern the best wide receivers prospects has become more of a crapshoot.

The randomness owes to a familiar culprit for NFL evaluators: the pervasiveness of the spread offense in college football. College football asks different demands of its wideouts than professional football. In college, wideouts have more specialized roles — most programs now feature an “inside receivers coach” and an “outside receivers coach” — and are asked to perfect a small complement of routes, mostly with the intent of catching passes in space. In the NFL, teams want their wideouts to be versatile and capable of running every route, often based on how the defense lines up, and the ability to wrest passes in heavy traffic is paramount.

“Offensive tackles and receivers are the hardest positions to evaluate now because of the influx of spread offenses and how defenses are having to play,” ESPN draft analyst Todd McShay told The Post’s Jesse Dougherty before the draft.

That is a bit of an oversimplification, but for wide receivers now, production in college translates less to production in the NFL. That makes it harder to gauge their impact in the NFL, which means it is riskier to use a high pick on one. Wide receivers in the first round will not become extinct — when the next physical freak in the mold of Julio Jones comes along, he’ll be easy to spot. But teams might follow the Cowboys’ path from Thursday night. Even if they need a wide receiver, it may make sense to wait a while to take one.

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