WALTHAM, Mass. — Jaylen Brown wasn’t in much of a hurry to leave the Celtics practice facility on the eve of his first career playoff game.

The rookie went through the hour-long workout with his team, and was the last one on the floor still shooting nearly 20 minutes after Celtics coach Brad Stevens called it a day. Brown then went back and had a meeting with his coaches, then came back out on the court and shot a bit more with assistant coach Micah Shrewsberry, before making his way over to two separate media sessions.

He has heard all about how the atmosphere will be unlike anything he’s ever experienced when the Celtics host the Chicago Bulls in Game One of their first-round series on Sunday night, and is eager to rise to that occasion.

“I’m ready,” he declared more than two hours after he first stepped on the practice floor Saturday afternoon. “I know I am ready. I am ready to go out and show I am ready to play in an atmosphere like this — that a rookie can hang out there with those guys.

“I am ready to show the coaching staff, the world, everybody that I’m ready to play.”

Brown realizes he is in a rare and fortunate position when it comes to NBA rookies. The third overall pick in last June’s draft is the only one of the top eight lottery picks to have his season extend past 82 games.

“I’m super excited,” he said. “Being a high draft pick and playing in the playoffs. What more could you ask for?”

As the Celtics look to defend their homecourt starting on Sunday, Brown should be an important variable in whether they elevate their collective game as a 53-win top seed playing a No. 8 seed with a .500 record, or whether they struggle against the veteran-laden Bulls, who underachieved during the regular season.

Boston went 26-10 this season when its “preferred” starting lineup — Avery Bradley, Jae Crowder, Al Horford, Amir Johnson and Isaiah Thomas — was healthy. But Horford said it is the youth of the Celtics who have the most remaining room to raise their ceiling in the postseason.

“A lot of our younger guys have really, really grown up,” Horford said. “I feel like still some of the younger guys haven’t played their best basketball yet — especially some of our bench guys like Jaylen and Terry [Rozier].

“I believe that once the playoffs start, they are due to break out.”

Like he does with everything Horford tells him, Brown said he took those comments to heart.

“Al is one of those guys who is very, very detailed in how he describes the playoffs,” Brown said. “I’ve asked Al a fair share. And I think he’s told me everything he knows about the playoffs. I think I’m prepared.”

Another veteran who helped Brown prepare for his rookie season coming into the year was Bulls All-Star Jimmy Butler. The pair worked out together in the offseason with Brown listening intently whenever Butler talked about his mental approach to the game, his game-day regimen and how he developed as a scorer early in his career.

Brown said he won’t hesitate to use some of the insights Butler gave him last summer to try to stop him over the next two weeks in the stretches where he will likely be assigned to guard the explosive scorer.

“Going against Jimmy, I’ve got to be smart,” he said. “No stupid fouls. Just keep your hands back because he will pump fake and draw fouls — him and [Dwyane] Wade. Just stay in front and make him earn whatever he gets.”

While Brown’s offense and shooting have improved over the course of the season — he is knocking down 3-pointers at a 40.9 percent rate (9-for-22) over his last eight games — his improved defense has been what has gotten him more minutes, and what will likely be the key to his court time against Chicago.

“I knew defense, when I got here, that was the only way I was going to get on the floor,” he said. “I had to pick that up quick. It was either that or sit on the bench. It was a sink-or-swim mentality. I gradually got better and better at it. I still have a long way to go.”

Brown also knows there will be no hiding defensively on the grand playoff stage, nor does he want there to be. The normally reserved and measured 20-year-old could hardly contain his anticipation of making his debut on that stage Sunday night.

“Going into the playoffs, where it matters the most,” he said, “I would hope I am at the point where I’m playing my best basketball.”