BOSTON - Every day of Ivan Rabb's freshman year at Cal-Berkeley was spent in the presence of Jaylen Brown. As his teammate, Rabb got to know Brown's tendencies on the court for the school's men's basketball team. And as his roommate, Rabb had the opportunity witness the promising young wing's mindset off the court.

Through this unique, intimate perspective, Rabb learned one thing about Brown: That he was destined for greatness at the NBA level.

"The main thing I noticed was his attitude toward the game," Rabb, now a rookie for the Memphis Grizzlies, told Celtics.com Monday morning before facing Brown's Boston Celtics at TD Garden. "Whenever he had a bad game, he took it real personal. He took the game very serious, he stayed focused and he always got in extra time in the gym to get better. He wanted to be great, and so he worked really hard."

During the 2015-16 NCAA season, the pair of top-five high school recruits led Cal to a 23-11 record and a No. 4 seed in the NCAA Tournament. The frontcourt duo parted ways at the end of the season, with Brown declaring for the 2016 NBA Draft, and Rabb opting to stay one more year at Cal before eventually being drafted 35th overall by Memphis in the 2017 Draft.

From afar, Rabb has watched with pleasure as Brown has begun to develop into the well-rounded NBA player Rabb knew he could become.

"His jump shot has gotten even more smooth," the 6-foot-10 forward said of Brown. "I think it was smooth in college, but it wasn't dropping as much, so he just continued to work at it. His form has always been good and now he's just knocking down shots. And everybody knows he can finish in the lane, so his complete game is coming out right now."

Brown's rapid development has led to a breakout sophomore campaign with averages of 14.1 points and 5.3 rebounds per game in a starting role for the Celtics.

Meanwhile, his former college teammate has been working diligently during his rookie season to carve out a consistent role of his own with the Grizzlies.

"It's been a year where I've been in the G-League and I've been back up with the big team," said Rabb, who has split 36 games equally between the G-League's Memphis Hustle and its in-town NBA affiliate. "Every day is something different, but I've gotten so much better. This last month and a half I've been with the big team getting minutes. I'm just capitalizing, trying to produce every single time I get on the floor."

Rabb says he's experienced many ups and downs along the way, but added that Brown's advice has helped him get through it all.

"He told me that I've gotta just listen to everybody's advice, especially coaches and players," said Rabb, who has been close with the Brown family since his youth. "And he said, 'Don't take things too personal, because sometimes it seems like they're picking on you, but they're not; they're just trying to make you better.'"

It seems like Rabb has taken Brown's advice to heart, because he's begun to establish a solid role with the Grizzlies. Over the last month and a half, Rabb has played 14 games with the NBA squad while averaging 14.1 minutes per night. He's used those minutes to the fullest by averaging 6.0 points on 66.7 percent shooting from the field, along with 4.1 rebounds per game.

Rabb's progress has impressed coach J.B. Bickerstaff, who allowed the 21-year-old forward to play a season-high 24 minutes Saturday night in Miami.

"He's a really good rebounder, he's a high IQ player and he's a very skilled player," said Bickerstaff. "He has the ability to make shots out to 17, 18 feet, and he's a much better passer than I thought he was. He can catch the ball on the elbows and guys can cut around him and he can get them the ball.

Added the coach, "I think the more that they play with him and understand that that's one of his strengths, the more they'll do it and we'll get more out of him."

The increase of playing time with the Grizzlies, as well as his strong play with the Hustle (15.2 PPG and 9.4 RPG), has boded well for Rabb's confidence.

"I think my stint in the G-League definitely helped boost me, being able to go out there and get reps," said Rabb. "And I think it's paying off now. The more and more practices, the more games I have, the more I have a better feel for the game. And it's been showing out there. So, I just want to continue with that process, and then next year make a huge leap."

Rabb is hoping that he'll be able to make a leap next season that's similar to the one that Brown has made this season. The process will continue for the rookie tonight in his highly-anticipated, first-time matchup against his former teammate, roommate and longtime friend.