Thomas had 18 in the second half, helping the Celtics rally from a double-digit fourth quarter deficit. He shot 11-for-21 from the floor and 4-for-7 from deep, contributing six assists and a steal.
The 76ers found themselves on top for most of the contest, thanks largely to 14 team blocks. Philadelphia — which remains winless at 0-16 — trailed 12-2 out of the gate, but ended the opening period on a 22-14 run.
The Celtics snapped a two-game skid with the W, improving their record to 8-7.
Turning Point: The Sixers held an 80-75 lead with 2:51 remaining, but watched the victory slip away following a 9-0 stretch by Boston. Jae Crowder gave the Celtics a two-point edge with a three at the 38-second mark, and Thomas sealed it with free throws later on.
A Hot Start Slows Down: Avery Bradley nailed three of his first four shots on the evening, but went just 1-for-11 from there. Bradley ultimately finished with 10 points, converting two of seven three-point tries.
No Inside Presence: The Celtics scored a measly 26 points in the paint, their lowest such total this year. On the other side, the Sixers had 38 — still not many but enough to make a difference.
Next Up: The Celtics host the struggling Wizards on Friday, hoping to gain some momentum before their upcoming road trip. Tip-off is at 7:30 p.m. ET, with CSN New England and CSN Mid-Atlantic calling the action.