ATLANTA -- A rash of untimely injuries placed Atlanta's postseason prospects in a freefall. And when the Hawks needed someone to stop the collapse, they called upon their returning All-Star.

Paul Millsap, playing just his second game since missing eight games with an injury, came up big again for Atlanta. The veteran forward had 26 points and 12 rebounds to help the Hawks enhance their playoff hopes with a 123-116 victory over the Boston Celtics on Thursday at Philips Arena.

It was the 19th double-double of the season for Millsap, who played his second game after missing eight with left knee synovitis. Millsap was 8 for 15 from the field, 9 for 12 from the line and added four assists in 29 minutes.

"The good thing about the first half was we got a bit of a lead and Paul played around 12 minutes," Atlanta coach Mike Budenholzer said. "Obviously, we needed him down the stretch."

The win moved Atlanta (40-38) a half-game ahead of Milwaukee for fifth place in the Eastern Conference. A loss would have dropped the Hawks, who lost nine of their previous 11, only one game above the playoff line.

Boston (50-29) lost for the second straight night, severely damaging any chance it had to win the conference. Atlanta won the season series against Boston 2-1. The second-place Celtics trail the Cleveland Cavaliers by 1 1/2 games for the top spot in the East.

"I thought we played pretty well in the second half," Boston coach Brad Stevens said. "Sometimes you feel like you found something in a loss and I feel like we can build off this one."

Atlanta also got 23 points from Tim Hardaway Jr., a career-high 20 points from Taurean Prince -- 18 in the first half -- and 18 from Dennis Schroder, who made three 3-pointers.

Boston was led by Isaiah Thomas with 35 points and Jae Crowder with 24. Marcus Smart made five 3-pointers and scored 18.

Celtics center Al Horford, who played in Atlanta from 2009-16, was beset with foul trouble and had only four points, five rebounds and three assists.

"Ball movement, definitely ball movement (was the key)," Millsap said. "Things we've tried to get better at all year. That's how we've got to play. This is our team and if we continue to do that, we will be able to score."

Atlanta began the game with more energy than Boston, which was coming off an emotional loss to Cleveland on Wednesday night. Prince scored Atlanta's first seven points and the Hawks bolted to a 14-point lead, going ahead 32-18 on a basket by Prince with 49 seconds left in the first quarter. Boston answered with a pair of treys by Smart and cut the margin to 32-24 after the opening period.

The Celtics got to within one point in the second period, the last time on a cutter by Bradley that made it 44-43 with 6:17 left.

Atlanta quickly answered. Back-to-back 3-pointers from Prince and Kent Bazemore soon restored the Hawks' 10-point lead and they stretched it out to 71-55 at halftime. It was the second-most points Atlanta scored in a half this season, exceeded only by the 72 it posted against Denver on Feb. 8.

"The first half is about as good of a first half as we've had," Budenholzer said. "I was really pleased with the way we came out."

The Hawks stretched the lead to 20 points in the third quarter when Howard drove past Horford on consecutive trips down the floor to make it 83-63. But the Celtics kept chipping away, went on a 12-3 run and got to within 99-89 when Smart connected on his fifth 3-pointer at the buzzer to end the third quarter.

"We just need to come out aggressive on the defensive end," Horford said. "We have to be better defensively."

Boston was within 121-116 after Avery Bradley made three free throws with 26.3 remaining. Millsap iced the game with a pair of free throws with 20.9 seconds left to restore a seven-point lead.

"It's the NBA and those guys made a run at us and came back to close it a couple of times, but I'm happy with the way our guys played," Budenholzer said.

NOTES: Boston coach Brad Stevens said he had no plans to rest the regulars before the playoffs begin. Atlanta did not start F Paul Millsap or G Kent Bazemore, both starters before injuries sidelined them. Millsap and Bazemore are available, but will play measured minutes until back to full strength. Atlanta was still without G Thabo Sefolosha, who missed his sixth straight game with a right groin strain. Sefolosha and F Kris Humphries were inactive for the Hawks. Boston's inactives were C Tyler Zeller and G Demetrius Jackson. ... Atlanta plays again Friday at Cleveland and returns home to host the Cavaliers on Sunday. Boston is at Charlotte on Saturday and finishes the season with home games against Brooklyn and Milwaukee.