Jeff Green's game-high 34 points included a key three-pointer that helped Boston hold on for a 98-93 victory over Detroit Pistons that secured the Celtics' NBA playoff berth.
Green made 13-of-19 shots from the field, including three three-pointers.
The victory, coupled with the Philadelphia 76ers' 88-83 loss to Charlotte, ensured the Celtics will be in the post-season for the sixth straight year.
Seven of the eight Eastern Conference playoff teams have now been determined, with the reigning champion Miami Heat leading the way.
Milwaukee remain in eighth position, six games in front of Philadelphia for the final spot despite falling 107-98 to the Minnesota Timberwolves on Wednesday.
In Boston, Paul Pierce and Brandon Bass scored 17 points apiece for the Celtics, with Bass adding a team-hig seven rebounds.
Pierce was back after missing Monday's game because of personal reasons, while Kevin Garnett missed his seventh straight game for Boston with an ankle injury.
Greg Monroe led the Pistons with 24 points and 17 rebounds.
In Milwaukee, Nikola Pekovic scored a team-high 27 points to go with eight rebounds to lead the Timberwolves to a victory over the Bucks.
Ricky Rubio had 19 points, 12 assists and eight steals and Derrick Williams scored 15 for the Timberwolves, who have been eliminated from playoff contention.
Ersan Ilyasova had 29 points and 12 rebounds and Monta Ellis added 18 points and five rebounds for the Bucks, who are staggering toward the playoffs having lost six of their last eight.