BOSTON -- Long after the practice court had cleared following a late October workout, Boston Celtics forward Marcus Morris could be heard playfully trash-talking rookie Jayson Tatum as the two engaged in spirited 1-on-1 work.

After Morris twice created space for a pair of midrange jumpers, Tatum finally generated a stop and extracted a bit of revenge against the veteran by repeatedly attacking the basket and using his length to finish layups with Morris, sidelined for the start of a season due to a balky knee, unable to fully contest.

Undeterred, Morris walked over to a pack of reporters after the battle ended and, in his soft-but-firm nature, proudly declared, "It felt pretty good beating a rook ass one-on-one."

Truth be told, Morris can't get enough of the rook. He sees a little bit of himself in the 19-year-old and says he yearns to provide the veteran leadership that Morris never received early in his NBA career.

"I had to learn on my own," Morris said. "Just coming from experience, just watching and seeing everything. ... Some rookies come in and think they know everything. [Tatum] was open."

"He's like a little brother to me," Morris added. "That's why I continue to be around him more and more. We just bond well. Younger players, sometimes your mind goes other places and sometimes things don't go right for you on the court. I just keep him encouraged."

What Morris really likes is the way Tatum plays the game. He loves the youngster's confidence, especially when he goes into attack mode, and he loves that he doesn't back down from challenges, like in that 1-on-1 session.

"That's what you want to see from young guys," Morris said. "When I got here, I saw how he holds himself, the swagger he's got. It reminded me of myself. He's a good kid and he's going to be around this league for a long time. ..."

"This kid, he's going to be a superstar."

AP Photo/Charles Krupa

With every trip to watch Tatum compete, Celtics president of basketball operations Danny Ainge walked away feeling as if Tatum had been the best player on the court. It happened the first time he saw Tatum live as a high schooler at the 2016 Nike Hoop Summit in Oregon and again during Tatum's lone season at Duke during the 2017 ACC tournament in Brooklyn.

"That two-day window [at the Hoop Summit], I thought he was the best player there among the Americans and the international players at the time," Ainge said. "He could shoot, he anticipated, he rebounded, he had length, he handled the ball. But what I really just liked was his poise. He had a great way about him."

As the Celtics' brain trust converged in Los Angeles in early June to watch a pre-draft workout with Tatum, the lingering question was whether the teenager was now the best player in the 2017 draft, for which the Celtics held the No. 1 pick, the result of a fortuitous swap with the Brooklyn Nets from the Kevin Garnett/Paul Pierce summer blockbuster of 2013.

The knock on Tatum to that point had been his perimeter shooting. But he had spent the break between the end of his lone college season and the start of private pre-draft workouts hoisting 250 3-pointers per day with hopes of being able to prove to NBA suitors that he could eliminate one of his few perceived weaknesses.

Then he went out in front of Boston brass and did just that.

It wasn't the tipping point for a Celtics staff that had Tatum in the conversation for the top pick throughout the draft evaluation process, but it certainly made them think a little bit harder about whether the lanky 6-foot-8 wing had the best chance of being the franchise-altering talent they craved.

A short time after that workout, the Celtics dealt the No. 1 pick to the Philadelphia 76ers, confident that Tatum would still be available to them with the No. 3 selection they received in exchange, while also picking up a potential future lottery pick for their troubles.

Now, three months into the season, Tatum has muscled his way into Rookie of the Year contender status.

Maybe most astoundingly, Tatum leads the NBA in 3-point shooting at a staggering 46 percent clip. According to Second Spectrum shooting data, Tatum has a quantified shooter impact (qSI) of 15.4 percent, meaning that he shoots 15.4 percent better on 3-pointers than an average player in similar situations (based on defensive pressure, shot clock, and shot type). That mark ranks him third in the NBA behind only the Chicago Bulls' Nikola Mirotic (17.5) and the Golden State Warriors' Klay Thompson (15.6).

"Right away you could just tell you're dealing with a guy that's not an average rookie."

"I guess the one thing that he did do in the pre-draft workout that he hadn't shown -- but I never really doubted -- was whether he could be a 3-point shooter," Ainge said. "I can't say I thought that he would be shooting the percentages that he has shot this year, but I felt, throughout his career he would get to this point. He had too good of a shot."

For the Celtics, it was a small glimpse into Tatum's beyond-his-years maturity and the way he yearned to be an impact player at the next level. For a front office that routinely debated whether the likes of Markelle Fultz, Josh Jackson or Dennis Smith Jr. were worthy of the No. 1 overall pick, it soon became clear that Tatum was their guy.

On Thursday night, the Celtics host the 76ers in the teams' fourth meeting of the season. Fultz seems likely to miss his 37th consecutive game while working his way back from what the 76ers termed scapular muscle imbalance and shoulder soreness.

Video of Fultz's new shooting motion is being analyzed with intense scrutiny. Thanks to the draft spot swap, the Celtics are positioned to collect a potential top-5 pick from the Los Angeles Lakers this year (if it falls between Nos. 2-5), or the Sacramento Kings' pick in 2019 (if it isn't No. 1).

Tatum's success, juxtaposed to Fultz's woes, only hammer home both Boston's shrewd drafting and trading activity. Tatum has started all 45 games this season for the Celtics, who sit comfortably atop the Eastern Conference with a 34-11 record.

As one NBA talent evaluator suggested recently, "Just imagine if the 76ers had a frontcourt of Tatum, [Ben] Simmons, and [Joel] Embiid right now. That's scary."

Instead, Tatum might be the biggest reason for optimism about Boston's future as a title contender. In fact, there might come a time in the not-so-distant future when Tatum is the best player on the court for the Celtics.

New Orleans Pelicans rookie Frank Jackson swears that Tatum's success shouldn't come as much of a surprise.

"I called this last year," said Jackson, who played with Tatum at Duke last season. "He's probably one of the most talented guys I've played with, at both ends of the floor. You see that now."

While the Celtics currently look like geniuses, Tatum wasn't a surefire No. 1 pick and most Boston fans had sold themselves on the idea of Fultz playing alongside Isaiah Thomas. But Tatum offered something the Celtics desperately needed: length on the wing and a scoring threat outside the guard position.

Celtics coach Brad Stevens noted how the idea of Tatum and second-year wing Jaylen Brown developing together grew mighty intriguing with Boston yearning to not only compete now but build a sustainable contender.

Even after a strong summer league showing, few expected Tatum to be an impact player this early. But Tatum earned a starting role even before Gordon Hayward's injury on opening night. He's averaging 13.8 points, the third-highest average on the Celtics' roster trailing only Kyrie Irving (24.1) and Brown (14.3).

It's not just the scoring for Tatum, but it's the way he's doing it with loud dunks and slick ballhandling. On Tuesday night, Tatum caught a pass on the wing in transition, went between the legs and behind his back with the dribble deftness of Irving while shaking defender Jrue Holiday then splashed a fading midrange jumper, much to the delight of the Boston bench behind him.