But the Hawks (15-10) made things difficult.
Garnett (18 points) converted the decisive field goal with a hook shot for an 85-84 advantage with 30 seconds remaining, then Kendrick Perkins blocked a Joe Johnson follow, and Rondo's free throw provided the deciding point. But Atlanta had two chances to tie. Johnson squandered one, hitting the first foul shot with 2.7 seconds on the clock, Garnett rebounding Johnson's miss on the second. Ray Allen then converted two foul shots with 0.7 on the clock. Mike Bibby's half-court toss then hit the front rim.
The outcome was in doubt until then, just as it was when the Celtics took a 103-102 victory over the Hawks last month in Boston on Paul Pierce's shot with 0.7 seconds remaining.
And though the Hawks took the first-round series between the teams to a seventh game last season, winning all three here, the Celtics keep having the last word.
"This is not a rivalry," Garnett said. "[The Hawks] are a very good team, they play with a lot of confidence and swagger. Joe Johnson is one of the best in the business and they cause a lot of hell and havoc. But you have to win for it to be a rivalry."
The Hawks seemed capable of victory. Though they started by misfiring from all angles, they kept firing and following, eventually flying into the lead until the final minutes.
"We didn't play great in a lot of ways but we just kept on grinding," said Celtics coach Doc Rivers. "They killed us on the glass and they got every loose ball. They got a lot of second shots but we executed down the stretch. This is a game in which we had to keep our composure."
The Celtics closed with a 22-13 edge over 6:41.
After a 3-pointer by Johnson (20 points) extended the Hawks' edge to 72-66 with 6:59 left, Garnett countered with a hook and a jumper, Pierce converted over Bibby, and Rondo finished a give-and-go from Garnett following a Perkins block for a 74-72 lead with 4:59 remaining, the Celtics' first advantage since early in the second quarter.
