The 37-year-old Garnett missed 19 straight games since Feb. 27 because of back spasms. The Nets went 14-5 over that span.
Garnett was back in the starting lineup and was sharp from the start. He scored on an alley-oop in the first quarter, made his first four shots, and had a nasty block on Michael Carter-Williams' layup attempt that knocked the rookie guard to the ground.
Garnett also passed Alex English to move into 14th on the NBA's career scoring list.
Coach Jason Kidd limited Garnett's minutes and the veteran center did not play in the fourth quarter.
Deron Williams had 19 points and Mason Plumlee 16 for the Nets.
Thaddeus Young led the Sixers with 20 points.
The Sixers, who had won two of four after losing 26 straight games, sliced a 21-point hole down to two after Henry Sims put back Carter-Williams' miss on his second free-throw attempt. With a chance to tie the game at 96-all on the next possession, Carter-Williams made 1 of 2 with 1:05 left.
Mirza Teletovic's first bucket of the game was a 3-pointer with 48.4 seconds left that gave the Nets some breathing room.
With starters Joe Johnson, Paul Pierce and Garnett on the bench, Williams helped the Nets seal the win from the line.
Garnett was loose and all smiles in the pregame layup line, slapping hands and offering encouragement to his teammates. Pierce took on Garnett in a brief 1-on-1 battle, and yelled "Welcome back!" as he blew by him to toward the basket.
Garnett is the no longer the dominant All-Star of his Minnesota and Boston days, averaging 6.7 points, 6.7 rebounds and 21 minutes in 49 games this season. But the layoff may help boost the life left in his legs that will be needed if the Nets are going to make any type of playoff run.
Garnett and Pierce turned back the clock on consecutive scores in the second - Garnett's big dunk was followed by Pierce's 3-pointer for a 13-point lead. The Nets led by as many as 21 before the Sixers made their run late in the fourth.
Garnett and Pierce had a seat on the bench during crunch time. That allowed the Sixers to pounce.
Carter-Williams went rim-to-rim off his own defensive rebound and finished with a one-handed dunk over Andrei Kirlenko. He helped the Sixers stay within 10 points of the Nets.
The Sixers closed within three when Williams was fouled on a 3-pointer with 3:08 left. He made the free throw for a 94-87 lead. Williams made all six of his free-throw attempts in the game.
Holis Thompson scored 18 points for the Sixers and Sims had 11 points and 11 rebounds.
NOTES: 76ers C Byron Mullens (sprained left ankle) was inactive. ... Johnson has made a 3-pointer in 25 straight games.
