Weeks ago, when Jadeveon Clowney visited Houston, first-year Coach Bill O’Brien looked the South Carolina pass rusher in the eye and wanted a promise.

“I’m going to stick my neck out for you,” Clowney recalled the coach telling him. “I need you to stick your neck out for me.”

Clowney, the physical specimen who altered opposing game plans and caused nightmares in offensive meetings for three college seasons, was scrutinized frequently for his motivation and effort. He was talented, sure, but how effective is a talented player who doesn’t always try? O’Brien wanted an assurance.

On Thursday night, with Clowney himself was wondering whether he had said or done enough to earn the Texans’ trust, Houston indeed stuck its neck out, selecting him with the first overall pick of the NFL draft. Clowney was the first defender taken first overall since North Carolina State’s Mario Williams in 2006, another defensive end selected by Houston.

Long after Clowney was taken, another star of this year’s draft, Texas A&M quarterback Johnny Manziel, waited until the Cleveland Browns — making their third trade of the evening — selected the Heisman Trophy winner with the No. 22 pick.

Throughout the 2013 college football season, few players faced as much scrutiny as Manziel and Clowney. The knock on Manziel, the exciting passer nicknamed “Johnny Football,” was his maturity; the worry about Clowney was his motor.

The former No. 1 national high school recruit had been both dazzling and frustrating, following mind-bending tackles by removing himself from the lineup and sitting out plays on the bench. He missed a Southeastern Conference game in 2013, a few months after being named a consensus all-American, and so the chatter began.

Sitting backstage Thursday, Clowney couldn’t help but wonder. “They can’t pass me up,” he recalled thinking. “They can’t pass me up.”

He was the first player taken of 30 invited to New York, a record number in the so-called green room at Radio City Music Hall. Among the players Clowney left behind was Central Florida quarterback Blake Bortles, who wasn’t seated more than a few minutes longer; he was taken by the Jacksonville Jaguars with the No. 3 pick.

That left the other quarterbacks, including Manziel and Louisville’s Teddy Bridgewater, to sit in that miserable fish bowl. Away went Bortles, the 6-foot-5 passer who will now play professional football about 140 miles from the school he led to a 12-1 record, the American Athletic Conference championship and a win against Baylor in the Fiesta Bowl.

“I had no expectations coming into this thing,” Bortles said. “I was pumped to be here, to be part of this atmosphere in New York City, and when I heard my name called, I was ecstatic.”

He might be the only one without expectations. The Jaguars, who three years ago selected quarterback Blaine Gabbert in the first round before cutting ties with him after last season, will look to Bortles to re-energize a fan base, fill seats at EverBank Field and maybe even provide an argument to keep the team in northern Florida.

All around Bortles and throughout the early part of the draft’s first round, teams loaded up on offensive weapons. Among the top 16 picks were four offensive tackles, perhaps the richest position in the draft, and three wide receivers. Auburn’s Greg Robinson was the top lineman taken at No. 2 overall with the selection the St. Louis Rams acquired two years ago when the Washington Redskins moved up to select quarterback Robert Griffin III.

Defense didn’t get much attention until the middle of the opening round, when five of six selections were defenders. One of those was the Chicago Bears’ selection of Virginia Tech cornerback Kyle Fuller, whose six interceptions and 33 pass breakups in four seasons made him the Hokies’ first opening-round defensive back since DeAngelo Hall in 2004.

That wait for defenders wasn’t especially surprising, but Manziel’s long night certainly was. The 2012 Heisman Trophy winner sat backstage, sipping water and checking his phone each time the cameras showed him, the smiles by those beside him growing more forced as each pick ticked away.

Manziel, the talented but undersized quarterback, spent most of last spring and summer toasting his Heisman win, shown often alongside celebrities at major sporting and entertainment events. Manziel had put on a different, more mature face following his redshirt sophomore year, which proved his electric first college season was no fluke.

Teams that needed a quarterback mostly sat in the top 10, and after Jacksonville took Bortles and Cleveland traded down five spots — and then, after another trade, took Oklahoma State cornerback Justin Gilbert — Manziel’s wait was on. It lasted nearly three hours, but he slid on his Cleveland hat, smiled and flashed the money sign with his fingers anyway as he walked onto the stage.

“I went into this knowing that everything would work itself out,” Manziel said shortly before Browns fans chanted “Johnny Cleveland!” during his news conference.

Bridgewater was the first round’s final pick; Seattle traded out of the 32nd selection, and Minnesota took the Louisville passer.

One player, though, had almost no wait. Clowney, who totaled 24 sacks in three seasons, appeared on “The Tonight Show” on Wednesday and took the call from Houston a night later.

It was a long way from Rock Hill, S.C., that fertile area of NFL talent — 11 of the small city’s natives have been selected in the previous 13 drafts — where Clowney grew up poor and promised himself and his family that better days lay ahead.

“A lot of people said I would never be nothing,” the 21-year-old defender said. “I kept saying: ‘I’m going to do something great.’ ”

Sure, he told O’Brien during that visit in Houston that he would work hard for him and quiet more doubters. “I’m ready, man. I’m not going to let you down,” Clowney said he told his future coach.

Whatever else he told O’Brien, it was enough to convince the Texans not to trade the top choice and select Clowney. Soon after it was made official, Clowney said he already has a few more goals in mind, no matter what anyone else might say. “Hopefully,” he said, “I’m going to be a Hall of Famer one day.”