Jaylen Brown reminds himself that this is what he wanted.

WALTHAM – Jaylen Brown reminds himself that this is what he wanted.

He wanted a big role on the Celtics as a rookie last year when he went through stretches of playing sparingly off the bench, and drifted in and out of the rotation. Rather than complain about it, he kept his head down, kept his mouth shut, and kept working for his opportunity.

Brown knew that opportunity would come this season as he entered training camp as a likely starter with only four returning players back from last year’s Eastern Conference finalist. Yet, he didn’t know there would be this much on him this soon with the catastrophic injury to Gordon Hayward, and with both Marcus Morris (knee) and Marcus Smart (ankles) out of the lineup.

“The mentality is the same,” he said following Monday’s practice. “It’s just the responsibility is different. I have the same mentality to come on the floor and produce. Have the mentality to come on the floor each and every night and do what’s asked of me. Be as consistent as possible.

“It’s a lot more strenuous on your body. It’s difficult guarding the best player every night and scoring the ball as well. It’s something I feel I am capable of doing and something I will get better at. I can’t complain about being in this position, because I’ve asked for that for myself.”

Through three games, Brown is the team’s second-leading scorer at 17.3 points per game, has led the team in minutes twice and is averaging 34:54 a game. He is second on the team in shot attempts behind four-time All-Star Kyrie Irving, second in 3-point attempts, and third in rebounds.

He has also been charged with being the primary defender on LeBron James and Giannis Antetokounmpo.

“I talked to coach and my responsibility is a little bit bigger,” Brown said as the Celtics prepared for Tuesday night’s game vs. the New York Knicks at TD Garden. “They’ll ask a lot of me, and I ask a lot of myself.”

With Celtics coach Brad Stevens calling Smart “day-to-day” after he did not practice Monday, and Morris saying Monday he is out for at least the next three games – targeting next Monday vs. San Antonio for a return – that means a lot of the burden for the team’s success over the next week will fall on the 20-year-old Brown and 19-year-old rookie Jayson Tatum.

“We’re both young, but pretty talented guys,” Tatum said. “He has a year experience. I’m just learning on the fly. We’re trying to push each other out there to help Al (Horford), and Kyrie, and Marcus (Smart) and Terry (Rozier), and those guys.”

Morris, who played one-on-one against Tatum for about a half hour after Monday’s practice, said he’s been impressed with what he’s seen from the pair of No. 3 overall draft picks.

“I constantly keep talking to them,” Morris said, “telling them: ‘Next shot, next play.’ They’re young. But at the same time they’re doing a great job of staying in the games and competing.”

Brown said has been able to lean on some of the things he learned from last year’s team as he’s been pushed to the forefront of this year’s rotation.

“A lot of the guys here are young, including myself,” he said. “But we’ve got to expedite this process. I was blessed enough to play on a team [last year] when I developed those habits learning how to win. Now we’re trying to help each other so we can be to the same level of expectations.”

Brown said he doesn’t pay too much attention to the outside expectations on himself – whether they were lower than he thought they should have been coming out of the draft, or rising exponentially each week in his second year. He said during preseason he was determined to be “unbothered” by the opinions of others who are not his teammates or those within the Celtics organization.

Now the task will be to block out those who cite youth and injuries as two reasons this team will fall short of its potential this season.

“It’s super important to stay in the moment,” he said. “Just breathe. There was a lot of pressure to get that first win [Friday in Philadelphia]. We wanted to get that first win. Guys have been a little flustered with everything that was going on.

“After everybody settles in to their role, settles in to what they have to do each and every night, and get comfortable with it, I think we’ll be fine.”

Scott Souza can be reached at ssouza@wickedlocal.com. Follow him on Twitter @Scott_Souza.