Joe Johnson scored 28 for Atlanta (6-1), finding an open Marvin Williams for the go-ahead 3-pointer with seven seconds left. But Pierce answered at the other end and the Celtics beat Atlanta in Boston for the eighth straight time, including all four in their first-round playoff series last spring when they took advantage of the home-court advantage to oust the Hawks in seven games.
Ray Allen scored 17, eight during an 18-2 run in the second quarter that turned a 44-28 deficit into a tie game at halftime. There were 12 lead changes in the third quarter as the game went back-and-forth, and the Celtics never led by as many as two baskets until Garnett hit a jumper from the top of the key, then grabbed a pair of rebounds before laying in an alley-oop that made it 92-88 with 3:33 to play.
Boston still led by four when Johnson hit a pair of free throws and then made a fallaway jumper from just outside the lane to tie it 99-all with 35 seconds left.
Pierce picked up a foul by driving to the basket and made two free throws, then Johnson drove and kicked it out to Williams for a 3-pointer from the right side to give Atlanta a 102-101 lead. Pierce got the ball, faked out a pair of defenders and put up the game-winner.
Williams' inbounds pass went through Mike Bibby's hands as time expired.
The Hawks led the entire first quarter, and took a 31-24 advantage when Flip Murray hit a 3-pointer at the buzzer. They scored eight straight points to make it 44-28 with 7:07 left in the half before Boston tied it at 46-all.
Notes: Last season, Atlanta took its first loss in its second game and didn't win its sixth until Nov. 28, the 14th game of the season. The Hawks started 11-0 in 1997-98. ... Murray had 12 points in the first half off the bench. ... Zaza Pachulia, who replaced Josh Smith in the lineup after he sprained his left ankle Friday night against Toronto, injured his left shoulder and left the game. ... Williams, who made one 3-pointer all last season, had four on Wednesday and is 8-for-11 this season.