Garnett, who declined interview requests, missed his 14th game of the season because of right knee ailments. Rivers said Garnett is expected to miss tomorrow night's game against Oklahoma City. With some solid practices, he could return Wednesday against Charlotte.
Glen Davis earned a double-double with 19 points and 12 rebounds in 43 minutes playing in place of Garnett.
"We just went out there and played basketball," Davis said. "No matter who's injured or who's hurt, we have to step up and play big. Our job is to go out there and play the game the way it's supposed to be played."
"We can't cry over spilled milk," added Paul Pierce, who poured in 21 points. "Hopefully, [Garnett] can just be healthy for the playoffs. Right now, that's the main concern. Kevin is going to do what he needs to do to get back out there. Meanwhile, the guys have to do what they need to do to step up."
Ray Allen scored a team-high 22 points and nailed three 3-pointers, and the Celtics received help off the bench. Eddie House had 12 points and hit 2 of 4 3-pointers, and Stephon Marbury scored a season-high 11 points. Atlanta's Josh Smith and Joe Johnson each had 22 points.
"They banged a little bit harder than we did, and they hustled a lot harder than we did," Hawks coach Mike Woodson said.
The Celtics had a 52-42 lead at halftime after Marbury nailed a 3-pointer with 1.8 seconds left. Boston made 6 of 12 treys in the first half, including three from Marbury and two from House. The Hawks were limited to 38.1 percent shooting in the half.
"We came out flat," said Hawks guard Flip Murray, who shot 4 of 13. "We didn't come out with any aggressiveness, and they outworked us."
The Celtics opened the third quarter with 7-2 run, topped off by an Allen jumper, to take a 59-44 lead. A second later, Woodson called time out. Boston finished the third with a 77-60 lead after a dunk by Davis.
