Boston, despite the absence of the suspended Rajon Rondo, clawed their way to a series-tying 87-80 victory at the Atlanta Hawks, while the Bulls, without the injured Derrick Rose, lost to Philadelphia in a 109-92 blowout.
Paul Pierce seized the mantle with 36 points and 14 rebounds as the veteran Celtics outscored Atlanta 26-14 in the fourth quarter to seize the game.
Boston trailed by 11 points late in the third but used an 11-2 run in the fourth to beat the Hawks, who got a team-high 22 points from Joe Johnson.
Rondo, who was suspended for one game for bumping into a referee, should return to the Celtics lineup on Friday for Game Three in Boston. Rose, however, has already been ruled out of the playoffs after he ruptured a knee ligament on Saturday.
Philadelphia's Jrue Holiday scored 26 points while Lou Williams added 20 as the 76ers played a high-tempo game and ran away from Chicago with a 36-14 advantage in the third.
Joakim Noah led the Bulls with 21 points. Game Three is in Philadelphia on Friday with the series tied 1-1.
(Writing by Jahmal Corner in Los Angeles; Editing by Greg Stutchbury; firstname.lastname@example.org; +64 4 802 7982; Reuters Messaging: email@example.com. For the sports blog Left Field go to: http://blogs.reuters.com/sport))