Pierce and Kevin Garnett, who were both traded to the Nets before the start of the season, received standing ovations from the Boston crowd ahead of the game.
"I had lumps in my throat and I tried to focus as much as I could," Pierce told reporters. "I'm happy we got it over with and I can go back to playing basketball.
"It was just a special thing for me. Through my bad times, through my immature times, through my growing up, becoming a man for this city and winning a championship."
Pierce was selected by the Celtics in the 1998 NBA draft and spent 15 years with the franchise.