Brown scored 34 points to lead the Celtics past the visiting Cavaliers 111-101 while Tatum added 18 and Robert Williams III had 21 points and 11 rebounds.
With the Celtics having seven players in Covid-19 protocols, they turned to 17-year NBA veteran Johnson -- who hadn't played in the league since 2018 -- and 15-year NBA guard C.J. Miles to fill out the roster and provide some wisdom to Boston's current superstars.
"Adding some older voices can't hurt," Brown said. "It can only help."
Johnson, who was drafted 10th overall by the Celtics in the 2001 NBA Draft, managed only two points in two minutes on the court but received huge applause for his comeback efforts.
"It's great to be back here 20 years later. It has been amazing to me. Still surreal but a lot of fun," Johnson said.
"I really appreciate these Celtics fans. It was exciting to get that kind of reaction. It's special."
Johnson was a seven-time All-Star who averaged 16.0 points in 1,276 prior games with Boston, Atlanta, Phoenix, Brooklyn, Miami, Utah and Houston.
He sees his role as advising Brown and Tatum as much as filling out the roster.
"Staying in their ear, making sure they know what they have to do for us to be victorious night in and night out," Johnson said.
Jrue Holiday scored 24 points and passed off 10 assists while Khris Middleton added 23 points as the reigning NBA champion Milwaukee
Bucks defeated visiting Houston 126-106.