Kevin Garnett had 22 points and grabbed 12 boards before fouling out with just under 3 minutes left in OT, and Brandon Bass, who also hit a jumper in OT, scored 21 points.
It was Rondo’s 19th straight game with double digits in assists.
Jeff Teague led the Hawks with 21 points and Josh Smith had 20 with 11 rebounds. The Hawks had won eight of 11 since losing to Boston at home on March 19.
It was the Celtics’ 11th win in 14 games. Pierce finished with 14 points.
Bass and Pierce hit jumpers, giving Boston an 88-84 lead early in the OT, but the Hawks sliced it to a one possession game on Kirk Hinrich’s open jumper.
The teams traded turnovers over the next 2 minutes — with the Hawks’ Smith getting picked cleanly by Pierce with 30 seconds to play, but the Celtics’ captain was called for an offensive foul on the other end with 10.1 seconds to go.
Smith front-rimmed a 3 and Boston gained possession after a battle for the rebound went out of bounds off a Hawks’ player in front of Boston’s bench with 1.3 seconds left.
Boston inbounded the ball to Rondo, who fired it in the air as the horn sounded. Pierce, just 6 of 19 from the floor, raised his arms in triumph.
In a back and forth fourth quarter during which the teams traded the lead five times, Boston went up 82-81 on Garnett’s jumper from the top of the key with 1:26 to go, but Zaza Pachulia hit one of two free throws on the Hawks’ next possession, tying it with 74 seconds left.
Bass then hit a short jumper in the lane and the Hawks’ tied it again on Joe Johnson’s jumper with 47 seconds to play.
Pierce, who struggled from the floor all night, missed a 3 but Garnett grabbed the rebound.
After Boston’s time-out, Garnett was forced to take a long fadeaway that missed the rim badly and the 24-second shot expired during a scramble for the rebound.
Teague front-rimmed a long jumper as the horn sounded, sending the game to OT.
Boston opened an 80-76 lead on Garnett’s 3-point play when he drove around Pachulia for a reverse layup and was fouled, hitting the free throw to cap a 7-0 spree with 4:04 to play. The Hawks then retied it on Teague’s jumper from the left wing a minute later after Johnson hit two free throws.
NOTES: Boston guard Ray Allen was sidelined by a sore right ankle that had him out a few weeks ago. He had played the last five games after being sidelined six by the troublesome ankle. … The teams’ final regular season meeting is on April 20 at Atlanta. … Boston returned in the early morning hours after a 115-107 win at Miami on Tuesday. … Pietrus suffered the concussion in a loss at Philadelphia on March 23 when he took a hard fall to the floor after he collided with Lou Williams and had to be taken off on a stretcher.