Joel Embiid said Tuesday night that he hasn't been having fun this season. It looked like he was having a blast at TD Garden Thursday.

In what was easily Embiid's finest game of the season, the Sixers ramped up their defense in the second half to beat the Celtics, 115-109.

Al Horford did not play against his former team as he's dealing with left knee soreness and left hamstring tightness.

Embiid was his dominant self and Tobias Harris had an outstanding second half in helping give Boston its first home loss of the season. The Sixers also did well to hold Jayson Tatum and Jaylen Brown to a combined 8 of 27.

Harris went just 3 of 11 in the first half, but he kept the aggressive mentality he’s shown lately. He attacked his mismatches, posting up Boston’s smaller players and taking their bigs off the dribble. He hit 7 of his 9 shots after halftime. He finished 10 of 20 overall for 23 points and also added eight rebounds, seven assists and two blocks.

It was a rough start for Simmons. He committed two early turnovers as the Celtics had a clear plan to clog the paint. The Sixers shot the ball well from three in the first half (9 of 17) and that did help open things up a bit for Simmons. Like Harris, Simmons did have a couple post ups to take advantage of smaller players. The Sixers playing better defense in the second helped Simmons push the pace a bit more, as well. Still, this was another lackluster game from Simmons offensively. He finished with just seven points and had six assists but five turnovers.

The victory improves the Sixers to 6-7 on the road and 19-7 overall. They've won 12 of their last 14. They’ll be right back at it again Friday night as they host JJ Redick and the Pelicans at the Wells Fargo Center (7 p.m./NBCSP).