Jerryd Bayless scored a season-high 21 points to help the Grizzlies win without point guard Mike Conley. Conley sat out with a sprained left ankle suffered in Sunday's loss to New Orleans.
The Grizzlies rallied from 17 down to take control late in the fourth. Bayless missed a jumper, Gay grabbed the rebound and put Memphis up 101-100 on a bucket with 13.3 seconds left. Philadelphia's Thaddeus Young missed a short attempt in front of the basket and the Grizzlies grabbed the rebound.
Gay hit both attempts from the free-throw line for the three-point cushion.
Nick Young couldn't get the tying shot off at the buzzer for the Sixers.
Tied at 79-all to start the fourth, neither team could break free the rest of the quarter.
Gasol hit a tiebreaking 3-pointer for a 93-90 lead but Evan Turner came right back with a short jumper and Thaddeus Young gave the Sixers a one-point lead after Memphis was whistled for an offensive foul.
Spencer Hawes hit a jumper and Jrue Holiday followed with basket after a fortuitous bounce popped the ball straight up off the rim and through the net for a 98-95 lead. It wasn't enough. The Sixers still haven't won consecutive games since they had a three-game winning streak from Nov. 25-30.
Turner scored a season-high 27 points, Thaddeus Young had 23, and Holiday had 18 points and 10 assists.
The Sixers need some good news.
Andrew Bynum, their 7-foot center, has targeted a post-All-Star break return from bone bruises in his knees that have sidelined him the entire season. The former Lakers All-Star, acquired in the offseason, dunked on Sunday for the first time with Philadelphia, a "baby step," in a comeback the Sixers are counting on to lift them into the playoff race.
Bynum sprinted at shootaround for the first time, and could practice by the end of the week.
Coach Doug Collins said Bynum can't wait to play.
"I think the most important thing is he's encouraged, that he's feeling better," he said before the game. "You can always tell when guys start feeling better. When you're hurt, you don't feel like you're part of the team."
He would have helped against Memphis.
Aided by near-flawless shooting, the Sixers had their highest-scoring first quarter of the season. They made 12 of their first 14 shots, including two 3s by Nick Young, and raced to a 17-point lead. A 44-percent shooting team, the Sixers made their first seven shots and led 33-20 at the end of the quarter.
Perhaps inspired by the sharp shooting, the Grizzlies came right back with a 14 of 18 second quarter, to take a 57-54 lead at halftime. Bayless was 7 of 10 for a season-high 19 points in the half. Not his high for a half. A game.
NOTES: 76ers G Jason Richardson (knee) missed his fourth straight game. ... Collins said he felt fine after leaving Saturday's game and missing practice the next day because of a sinus infection and blocked nasal passage. ... 76ers C Lavoy Allen needed stitches in his upper lip. ... Grizzlies F Zach Randolph had 12 rebounds.