Kevin Garnett had 21 points and 12 rebounds on Saturday and the Celtics handled the Nets, 94-82.
Boston, seeded fourth in the Eastern Conference, clinched a playoff berth with the win and a Milwaukee loss to Indiana later Saturday. The third-seeded Pacers lead Boston by three games.
Avery Bradley and Brandon Bass both scored 18 for the Celtics, who fell to the Raptors in the opener of a back-to-back-to-back road stretch on Friday. They moved 3 1/2 games ahead of Philadelphia and New York in the Atlantic Division with Saturday's win.
Gerald Green had 15 points to lead the Nets, who were coming off of a victory over the 76ers. Deron Williams and Jordan Williams both scored 12. Deron added 14 assists and Jordan finished with 14 rebounds.
The Celtics opened the second half with a 9-0 run, turning a tie game into a 57-48 advantage.
Later in the third, Bradley knocked down back-to-back corner threes, stretching the lead to 69-57. He added another trey before the quarter ended and Boston was up 74-61 entering the fourth.
In the final quarter, the Celtics stretched their advantage to as many as 17 and were not threatened down the stretch.
The Nets had led by as many as nine on the first and were up 28-22 after one. Late in the second, Boston grabbed the lead, 37-36, on Bradley's layup, but Green knocked down a deep three at the buzzer for a 48-48 tie at the half.
Celtics point guard Rajon Rondo had 15 assists and has now handed out 10-plus assists in 21 straight games...Ray Allen missed his third straight game for Boston with a sore right ankle...Jordan Williams' 14 rebounds marked a career- high.