Sealy wore No. 2 as a member of the Minnesota Timberwolves.
Garnett wore No. 21 for 12 seasons with the Timberwolves and No. 5 for six seasons with the Boston Celtics.
"There was two reasons," Garnett said Thursday, regarding the uniform change. "My chapter in Minnesota was 21. My chapter in Boston was 5. And 5 was not available [here].
"It was only right to [honor] someone that I respected so much and have a lot of respect for who he is as a person more than anything. It was only right to pay homage to a dear friend of mine."
No. 5 was presumably unavailable because first-year Nets coach Jason Kidd wore that number when he was the franchise's star player in New Jersey.
Garnett and Sealy were Timberwolves teammates and close friends. On May 20, 2000, Sealy was driving home from Garnett's 24th birthday party when a pickup truck traveling on the wrong side of the road collided with Sealy's SUV, killing Sealy.