It seemed like Jrue Holiday was joking when he said last week that Joe Mazzulla would probably put the Celtics through some “crazy ass drills” to keep them sharp during the week off leading into the playoffs.

But maybe he wasn’t joking.

The Celtics returned to the Auerbach Center practice floor on Tuesday, and with a week off and their first-round opponent still unknown, the session was intense.

“Probably harder than any training camp practice we had,” Al Horford said. “Just a lot of pace. It was very productive.”

That was by design. The practice was closed to the media, but it lasted at least two hours and the session could be heard loudly through closed doors. There was pumped-in crowd noise and in-arena music blared through the speakers consistently to simulate a game atmosphere. Derrick White said the practice included toughness drills and moving without the ball.

With a playoff run that is expected to reach June, Mazzulla wanted to reset the standard.

“That’s what today is, a training camp for the playoffs,” Mazzulla said. “Everyone goes back to square one, you got to reestablish the habits and the things you build throughout the year. At the same time, don’t take them for granted. I thought the guys did a good job, with the physical and mental approach to a day like today.

“Today’s like the first day of a long journey, however long that may be.”

The first chapter will start on Sunday with Game 1 of the first round, but the Celtics will have to wait until Friday night to know who their opponent is. The 76ers face the Heat on Wednesday for the No. 7 seed. The loser will face the winner of Wednesday’s Bulls-Hawks game on Friday to determine the No. 8 seed, who will play the Celtics.

Until then, there’s not much the Celtics can do other than work on themselves.

“I think it’s as simple as, regardless of who you play in the playoffs, it’s no different than the regular season,” Mazzulla said. “It comes down to the margins, the style, and the system in which we play. That’s really what it is. So between now and Friday, we’ll hammer home us getting better as a team, and how we can continue to work the margins on both ends of the floor. And understand the playoffs, there’s obviously more attention on it, but winning a basketball game comes down to all the same things.”

White next?

From the day Holiday stepped foot in Boston after his sudden trade on the eve of training camp, Brad Stevens has seen a selfless player willing to do whatever it takes in pursuit of another championship. On a loaded team that includes multiple All-Stars, he’s proven to be a great fit and easy decision to retain as the Celtics locked him into a four-year extension last week.

“Jrue came here, joined our team, and all he tried to do was add to winning,” Stevens said. “And for a guy that is as accomplished as he is, that’s used to more usage, more reps, more touches, and all those other things, that never even came into play. All that came into play was, what kind of a teammate am I being and can I help us win? …

“I’ve been really impressed with Jrue and I think that, as you look at a person like him, and you think about the long term of a group, you think, obviously, you need really good players and guys that can play on both ends of the court. But you also want people that the young players can look up to and he is a person they should look up to, and certainly do look up to.”

With Holiday, Jaylen Brown and Kristaps Porzingis already extended, and Jayson Tatum likely to receive the supermax this summer, four of the Celtics’ five starters are locked up long term. That means White – who has one year remaining on his contract – is next up for an extension. The C’s certainly want to keep as much of this championship-level core intact as possible, but it will come with an even steeper price if they extend White.

“I can’t talk about much with things that we’re not allowed to discuss until July 1,” Stevens said. “Derrick’s having an amazing year. Derrick’s a huge, huge part of our team and we want him around for as long as we can keep him around.”

Griffin retires

Blake Griffin officially announced his retirement from basketball on Tuesday after 13 seasons, with his last one coming with the Celtics in 2022-23. He didn’t return despite his former teammates trying to lure him back.

Griffin, the No. 1 pick in 2009, signed with the Celtics during training camp last season after six All-Star appearances and five All-NBA selections. But the then-34-year-old was self aware that his prime was behind him, and embraced a smaller role. He was beloved in the Celtics locker room.

“When we first signed him, I was a first-time head coach and I’m coaching a former No. 1 pick. See how this goes,” Mazzulla said. “And I really didn’t know him that well and I really grew to have a level of respect for him. When we decided to kind of go away from him, he came in and pulled me aside and said, ‘Hey, what can I do to get back? What can I do to get better?’ So for a guy of his stature and of his resume and success, his longevity of a career, to come to a first-time coach and ask that, just said a lot about who he was.

“I think from that point on, he kind of took control of the temperature in the locker room. So that was a moment I’ll never forget and I’m really grateful I got to be around him.”

Horford also deeply appreciated his time with Griffin.

“The year that he was here, he made it enjoyable for me,” Horford said. “It was just fun to come into work with him every day and getting to talk to him and getting to know him. Some of the things off the court, and him as a person. Just a great guy. Definitely Hall of Fame player with everything he’s accomplished. I’ll make sure that I reach out to him. At some point, we’ll celebrate because he had an unbelievable career.”