BOSTON (AP) -- Rudy Gay hadn't hit a game-winning shot since high school.
The Grizzlies squandered a 17-point fourth-quarter lead, but Gay bailed them out when he took Mike Miller's pass and sank a 15-foot jumper from the top of the key with 2.6 seconds left.
The play was designed for Miller to put the ball on the floor, but Gay's defender, Gerald Green, collapsed on Miller as he went to the hoop, leaving Gay wide open.
Gay, who said he last hit a game-winner in the county championship as a senior at Archbishop Spalding High School in Severn, Md., took Miller's pass and calmly sank the jumper for his eighth point of the night.
"I knew it was going in," Gay said. "I didn't feel like it was the end of the game at all, it just felt like any other jump shot I've took."
Sebastian Telfair missed a long 3-pointer at the buzzer for Boston, which lost its fourth straight.
Chucky Atkins scored 19 points and Lawrence Roberts added a career-high 18 points on 14-of-15 from the free-throw line for the Grizzlies, who snapped a three-game losing streak and improved to 2-9 on the road. Memphis' other road win came in Denver on Nov. 28.
"It feels good for us to win on the road," Atkins said. "I think this needs to carry over. We need to take what we did tonight and build on it next game."
Paul Pierce scored 25 points and Green scored 16 of his 21 points in the fourth quarter for the Celtics, who have lost six of seven.
"A lot of people are saying that I played a pretty decent game, but I don't feel like I did," Green said. "I feel like it wasn't good enough because we lost. I have to have that mind frame. At the end of the day, we gotta win the game."
With Boston trailing 90-73 midway through the fourth quarter, Green scored 12 during a 21-4 run that tied it. Delonte West's 3-point play completed the comeback with 40.4 seconds remaining, but after the team traded baskets Gay got open from beyond the free-throw line for the winner.
Playing without Wally Szczerbiak, who missed his second game with a sprained left ankle, the Celtics struggled on offense until the closing minutes. The Celtics turned the ball over 21 times for 28 Grizzlies points.
Boston was also without center Kendrick Perkins, who sat out with plantar fasciitis.
"We're undermanned, so what?" Celtics coach Doc Rivers said. "No one's going to feel sorry for you. If you hang your heads, they're going to attack you. And that's what they did."
The Grizzlies shot 21-of-23 from the free-throw line in the first half to take a 46-44 halftime lead despite shooting 33 percent.
After Ryan Gomes' layup gave Boston a 52-50 lead early in the third quarter, Memphis went on a 13-2 spurt to take a big lead. Hakim Warrick tied it 52, Stromile Swift made a pair of free throws on the next possession to put Memphis up and Dahntay Jones capped it with a short jumper give Memphis a 63-55 lead with 3:07 remaining in the period.
Jones had 18 points, Warrick had 12 and Miller had 12 points and eight assists for Memphis.
Boston used its sixth starting lineup this season. ... Memphis point guard Damon Stoudamire returned after missing four games with a sore right knee. ... It took Boston forward Brian Scalabrine just one quarter to surpass his previous season high in points and rebounds. Scalabrine, who finished with 10 points and eight rebounds, had seven points and five rebounds in the first. ... Memphis shot just 4-of-16 in the first quarter and trailed 28-19. ... Szczerbiak could return as soon as Friday, while Perkins could miss up to four weeks, Rivers said before the game.