In a down year so far in the Atlantic Division, the Raptors (5-7) wrested away first place from the Sixers (5-8).
DeRozan and Gay dominated the Sixers in the second half to turn this one into a rout. Gay hit a pair of 3-pointers and scored 15 points in the third quarter, and DeRozan scored 30 points through the first three quarters to build a 16-point lead.
The Raptors may not have a winning record, but they have themselves in first place.
The Sixers held that spot thanks to a surprising 3-0 start. But reality has set in for a team that was expected to rank among the worst in the NBA.
Spencer Hawes hit his first nine shots and finished with 28 points and 10 rebounds for the 76ers.
Philadelphia's fourth straight loss came on the heels of an 0-3 road trip. The Sixers started Daniel Orton and James Anderson, and a bench made up of Hollis Thompson, Brandon Davies and Lavoy Allen is one of the weakest in the league.
Led by DeRozan, the Raptors pulled away to a 55-48 halftime lead. He hit three 3s in the half and scored 22 points, putting him on pace to top his career high of 37. He didn't slow down in the second half as much as it was his teammates simply taking turns dominating the ball.
Against a woeful defense, the Raptors shot 12 of 21 on 3-pointers through three. Terrence Ross, who had 17 points, and Steve Novak ended the quarter with consecutive 3s to close a 15-5 run.
Hawes was the only Sixers player who at least was able to make this one a game. He hit his first five free throws and his first three 3-pointers to keep it close. Hawes finally missed a free throw in the third, only to have Allen put it back for a bucket that cut it to 76-70. The Raptors wouldn't let the lead dip below six points the rest of the way.
DeRozan was fouled on a 3-point attempt late in the fourth and hit all three free throws to make it 107-92 in front of an almost empty arena.
The Raptors were just the latest team to put up big points against the Sixers, who have allowed 100-plus points in 11 of 13 games this season.
Michael Carter-Williams returned to Philadelphia's starting lineup after missing the previous four games with a bruised left arch. He scored 10 points. Evan Turner had 13 points and 10 rebounds.
NOTES: 76ers F Thaddeus Young missed the game for personal reasons. ... Raptors G Kyle Lowry, a Philadelphia native who played at Villanova, had most of the team over for a family dinner Tuesday night. He had 13 points and 10 assists. ... The 76ers waived F Kwame Brown and G Darrius Morris. They signed free-agent guards Elliot Williams and Lorenzo Brown. ... 76ers coach Brett Brown was whistled for a technical.