BOSTON — The Boston Celtics made the first move of this year’s NBA draft days before it began when they traded the No. 1 overall pick to Philadelphia in a move to add to an already rich cache of future selections.

On draft night, they still grabbed one of the most NBA-ready players available.

Boston selected Jayson Tatum with the No. 3 pick Thursday, adding a 6-foot-8 small forward who was a polished scoring threat during his lone season at Duke. The 19-year-old was a third-team All-ACC selection, averaging 16.8 points while shooting 45.2 percent from the field.

“He’s a really skilled player, really talented scorer,” said Celtics Coach Brad Stevens. “Great kid, great work ethic. We’re excited to have him aboard.”

It was the second straight year the Celtics have chosen third overall. Boston selected Jaylen Brown with its first round pick in 2016.

Tatum said he feels fortunate to be joining a contender immediately.

“It’s great,” he said. “I think that I get to learn that much more, especially from a veteran team that knows what it takes to get there. I can’t wait to go and learn from Coach Stevens and Isaiah Thomas and just everybody on that roster.”

As part of the deal with Philadelphia, Boston will also receive a first-round draft pick in either 2018 or 2019 – giving it even more bargaining chips to bolster its roster with a trade.

With their three second-round picks, the Celtics draft SMU forward Semi Ojeleye, Arizona guard Kadeem Allen and California guard Jabari Bird.

Tatum gives the Celtics some immediate rotation flexibility, with the ability to play both forward spots and defend as many as four positions.

“I think the biggest thing is that we really value his versatility,” said Stevens. “A couple years ago, I talked about how we were thin on guys that could play a number of different positions, when you talk about, really, 2-3-4. Now we’re starting to really – we’ve got a lot of position-less players that can dribble, pass, and shoot. That’s a good thing.”

The Celtics have been high on Tatum throughout the draft process and brought him in for a private workout late last week. Tatum said he stayed in contact with Duke Coach Mike Krzyzewski throughout the draft process, and it was Coach K who encouraged him to take the Celtics up on their invitation.

“He was just ranting about how great of a person Brad Stevens is,” Tatum said. “He really wanted me to go up there and work out for them. I was all for it. It worked out.”

Boston also brought in No. 1 pick Markelle Fultz, but drafting the Washington product would have likely meant a move from point guard to shooting guard, with an All-Star point guard in Thomas already on the roster.

It made Tatum not the compromise, but the best fit for a team that’s still in position be a big player in free agency this summer.

“I think that he’s a guy that we thought really highly of from Day 1,” Stevens said. “When I kind of got reintegrated into this process, right after the season was over, he was one of the guys that it was clear that we were targeting.”

Celtics president of basketball operations Danny Ainge said he felt comfortable trading the top pick to the 76ers because he thought the player he planned to take at No. 1 would still be around at No. 3.

He turned out to be correct.

“That’s a great compliment, especially with all the great guys in this class. The two guys that went ahead of me, they’re great players, but I’m glad at how it worked out, so I’m happy,” Tatum said after he was chosen behind Fultz and Lonzo Ball, who was drafted by the Lakers with the No. 2 pick.

Shortly after Tatum was selected, several sources reported that the Celtics were engaged in trade talks with the Indiana Pacers to acquire all-star forward Paul George, who has one year left on his contract before becoming a free agent. Those talks stalled, however, with the Celtics apparently unwilling to meet Indiana’s asking price for a player who has said he wants to sign with the Lakers after this upcoming season.