WALTHAM, Mass. — Last October, he was a freshman at Duke University preparing for life with Coach Mike Krzyzewski.

A year later, Jayson Tatum was getting his feet wet in the NBA.

And it was no surprise that the Celtics rookie forward was dealing with some nervousness in a preseason game Monday night at the TD Garden when he first stepped onto the court midway through the first quarter against the Charlotte Hornets.

“I think it was mostly butterflies in my first game,” said Tatum. “I was definitely nervous and excited when I first got out there.

“I don’t know if anything surprised me. I was living in the moment, like, ‘Wow, this is my first NBA game.’ That’s what I was thinking when I walked on the floor.”

Tatum and Marcus Smart were the first players used off the bench by Coach Brad Stevens.

It was obvious in the beginning that Tatum was trying to get used to a new situation, but as the game went on, he became more comfortable.

“I was just more relaxed after I got the first half out of the way,” said Tatum. “Guys were telling me to just breathe and relax and let it come to you and I think that’s what happened.

“It felt good. I was anxious at first, but as the game progressed I felt a lot better.”

Tatum played a game-high 33 minutes, scoring nine points on 4-of-11 shooting while grabbing five rebounds and handing out five assists in addition to blocking two shots and getting two steals.

Stevens wanted to get a long look at Tatum, the third player taken in the draft last June, and he will probably feature him in the rotation.

Getting Tatum on the floor right away in the opening quarter was a good sign for him.

“Hopefully it’s a good thing,” said Tatum. “I’ve been playing well in practice, so hopefully it means I’m going to play in the game.”

Tatum, who turns 20 next March, has plenty of talent, but Stevens knows there’s going to be ups and downs, just like Jaylen Brown experienced in his rookie season a year ago.

“The bottom line is he can get so much better and he’s already a good player,” said Stevens. “There are plenty of things he did well and there are plenty of things he can improve on, but he’s got a good attitude about it.

“I think he’s a lot like Jaylen from the standpoint I don’t think he’s going to get too high or too low. He’s got a really even keel about him.”

Tatum has already drawn high praise from Al Horford and Kyrie Irving, and he is thankful for their guidance.

• Forward Marcus Morris, acquired by the Celtics for Avery Bradley in July, was found not guilty of aggravated assault Tuesday in Arizona.

Morris and his twin brother, Markieff, were charged in connection with a 2015 assault of Erik Hood.

The trial took place throughout training camp, so Morris will likely have his first practice with the Celtics on Thursday morning before the team heads to Philadelphia to play the 76ers Friday night.

FOR CAVALIERS Coach Tyronn Lue, the shooting in Las Vegas became personal.

Lue said he personally knows three people who were shot Sunday night when a gunman opened fire on a crowd of 20,000 concert-goers, killing 59 and wounding more than 500.

Lue, who has lived in Las Vegas over the past nine summers, said he knew about 15 people who were at the show.

“Just a horrible thing to have to go through, especially when I lived there for nine years and knowing all the people I know out there that work at the Mandalay Bay and Aria,” Lue said Wednesday night before the Cavs hosted the Atlanta Hawks in their first exhibition game. “I feel sorry for all the loved ones of each one that lost someone or been badly hurt. It’s just not a good thing. I’ve been touched by a few people who’d gotten injured, who’d gotten shot. Just a tough position to be in.”

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