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Mere minutes into his first Las Vegas Summer League practice with the Phoenix Suns in 2015, Earl Watson, then a newly hired development coach, was fluttering around the gym. He'd seen glimpses of Devin Booker, then all of 18 years old, and had to share the gospel.

"It just hit immediately," Watson said. "You could tell by his demeanor, his confidence, his calm, his drive, his courage."

After two thoroughly dominant offensive displays by Booker over the weekend—38 points against the New Orleans Pelicans on Friday and 39 points against the Los Angeles Lakers on Sunday—the world is starting to see what Watson and the Suns front office saw leading up to the 2015 draft.

Like everyone else, they were impressed by Booker's sweet stroke through his freshman year at Kentucky. But it was the way he handled the spotlight that set him apart.

"Every time he went out there, he wasn't a wide-eyed kid overwhelmed," said Pat Connelly, Phoenix's assistant general manager. "He looked like he could handle any situation thrown at him, which isn't normal because most 19-year-olds or 18-year-old kids—18 in his case—are allowed moments where they kind of get overwhelmed."

When Booker was still on the board at No. 13 during the 2015 draft, the Suns pounced, even with a pair of highly paid guards (Eric Bledsoe and Brandon Knight) already on their depth chart.

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After scoring 14 points during a season-opening loss to the Dallas Mavericks, Booker sat...and sat...and sat some more. Head coach Jeff Hornacek would call Booker's number from time to time, but the rookie—then also the youngest player in the NBA—saw his minutes fluctuate wildly through his first seven weeks as a pro.

"Those are some of the worst days at the beginning of the season last year when I wasn't playing at all," Booker said. "I just never want that feeling again. So when I stepped on the court, I just did everything it took to be out there on the court."

Off the court, Booker found other ways to test himself. He blew through his coaches' shooting drills and then concocted new games for himself. After practice, he would challenge every player in the building to a game of knockout and wouldn't leave until he won.

"He might not ever admit it, but I knew he wanted to make sure that the belief that he belongs on the court had substance to it, that it was backed up," Watson said. "By winning these games, it kept him believing that, 'OK, I belong in this league and I belong on the court.'"

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Piece by piece, the Suns crumbled around Booker.

In December, Bledsoe went down with a knee injury—his second in three seasons with Phoenix. Less than a month later, Knight strained his groin. Hornacek bickered with Markieff Morris, saw his top two assistants fired and then got the axe himself in early February.

"I learned a different side of this game," Booker said. "When you watch it growing up, you're just a fan of basketball. You don't realize there's a business behind it, and I figured that out quick."

In the span of eight months, Booker had gone from an 18-year-old buried on the bench to the Suns' primary playmaker, and Watson from a player-development novice to interim head coach.

"I had never experienced anything like that, and it was my 16th year," Watson said. "[Booker's] seen the worst and it can only get better."

Booker first broke through as a sharpshooter, nailing 58.8 of his threes through his first 26 games. Once Bledsoe and Knight went down, he had to run the Suns offense. The minutes piled up, along with the turnovers and bricks.

Watson and his staff tutored him on when to shoot, when to pass and when to dominate, and then they let him learn on the job in live action.

The Suns could barely buy a win, but Booker excelled. He put up 32 points opposite Paul George, 27 against Kyle Lowry and DeMar DeRozan, 34 across from Dwyane Wade, 28 more in a win over his idol Kobe Bryant. By the end of his rookie season, he had logged 51 starts, averaging 17.4 points and 3.5 assists in 34.1 minutes during those games.

"To me, the biggest thing is he plays with a really good pace," said Utah Jazz head coach Quin Snyder. "You can't speed him up."

From the rubble of Phoenix's 23-59 campaign rose Booker's first-team All-Rookie selection.

Booker followed up that franchise-changing campaign with a summer full of fun.

He and D'Angelo Russell, a close friend of his from their AAU days, vacationed together with their brothers in Mexico shortly after the season ended. He represented the Suns at the NBA draft lottery in New York. He spent draft day in Chicago with Tyler Ulis, another youth basketball buddy and former Kentucky teammate, who dropped into Phoenix's lap at No. 34.

Aside from two weeks at home in Grand Rapids, Michigan, there was a visit to Churchill Downs for the Kentucky Derby, a stop in Los Angeles for the ESPYs and a trip to Toronto for Drake's OVO Fest. When the Canadian rapper came through Phoenix on his tour, he asked Booker for his jersey.

Then, to Booker's surprise, Drake wore that black No. 1 on stage at Talking Stick Resort Arena.

"That's somebody that I idolize outside of the basketball world," said Booker, who first met Drake at Kentucky's annual Big Blue Madness. "Living legend. I like seeing greatness, too. He's like a big brother to me. It was a crazy moment."

Booker didn't let the spoils of NBA life distract from what put him on the map in the first place.

"It's a dream come true for me," he said, "but we do realize that it all starts on the court."

In between his guest appearances, there was basketball, and plenty of it.

Open runs with the Arizona State squad in Tempe. Skill work with Suns coaches at the team's facility in Phoenix. Scrimmages against the world's best players at Team USA's pre-Olympics camp in Las Vegas. Two-a-days—three-a-days, if you count the weightlifting sessions—with his trainer, Robbie Haught, back in Michigan.

Booker had to get stronger to contend with the rigors of an 82-game campaign as a potential star. He had to work on his pick-and-roll skills to sharpen his execution of the Suns offense under Watson. He had to tighten his defense to ensure he'd shine on both ends.

Above all, he had to develop his voice to allow him to lead others with his words and his actions.

"When that time is right, we encourage it, we embrace it," Watson said. "But he has to own it. It can't be forced. So we want to empower him to own it."

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The morning before the Suns opened their preseason against the San Antonio Spurs, Watson had an announcement to make. Bledsoe, back from another knee operation, would once again be the starting point guard.

His partner? It wasn't Knight—who cost Phoenix a top-three-protected pick from the Los Angeles Lakers in a trade and another $70 million over five years in restricted free agency—but Booker.

That night, Booker scored a team-high 19 points in a 91-86 win, however meaningless, over the Spurs. Two games later, he torched the Portland Trail Blazers for 34 points.

"I had to keep reminding myself that he was only 19," Blazers head coach Terry Stotts said. "Because he looked like a veteran out there, getting to his spot and playing with a lot of confidence."

Now that he's solidified a starting spot, Booker's work ethic, confidence, skill and attitude will dictate how much further he climbs.

Soon enough, he might be the face of the Suns, too.

Over the summer, Watson described the baby-faced guard as "an old soul in a young heart." Before an early-season loss to the Los Angeles Clippers, he talked about Booker as "the biggest part of who we are"—even though the youngster sat out that game with a toe injury.

That's a lot to put on anyone's plate, let alone that of someone who's not yet old enough to order a beer.

"You come in as a rookie, you're just trying to keep your head above water," said Clippers forward Blake Griffin, who stepped into a similarly central role by the time he was ready to play in 2010. "As a rookie, you just try to play as hard as you can to make up for your mistakes and all the things you don't know. Every year, you just try to add to that."

To that end, Booker is well on his way.

"I always knew I was capable of this," Booker said. "I didn't know I'd get this opportunity this early, but I knew I'd have my opportunity. And when it came, I wasn't looking back."

All quotes obtained firsthand unless otherwise noted.

Josh Martin covers the NBA for Bleacher Report. Follow him on Twitter, Instagram and Facebook.