Al Harrington contributed 15, Tracy McGrady scored 14 and Wilson Chandler had 12 points and 11 rebounds for the Knicks (24-43), who snapped the Dallas Mavericks' 13-game win streak with a convincing 128-94 victory last Saturday.
David Lee grabbed 16 rebounds as the Knicks improved to 2-2 on this five-game road trip.
Jrue Holiday scored 18 points, Willie Green added 17 and Andre Iguodala had 14 points and a career-high 17 rebounds for the Sixers (23-44), who have dropped five in a row and 10 of their last 11. The Sixers are just 10-22 at home.
Samuel Dalembert had 11 points and 18 rebounds for Philadelphia.
After Holiday made a layup to get Philadelphia within 85-82 with 3:47 left, Douglas knocked down a 19-foot jumper and Gallinari connected on two free throws for an 89-82 advantage with 2:03 remaining.
Iguodala missed a runner in the lane and Gallinari responded with a 3-pointer for a 10-point lead. The 7-0 run sealed New York's second consecutive win in Philadelphia for the first time since 2004.
Iguodala shot only 5-of-22 and missed all seven of his 3-pointers. Over his last four games, Iguodala is 1-for-19 from 3-point territory.
Trailing by nine points midway through the third quarter, the Knicks went on an 11-0 run to take a 67-65 lead with 2:31 remaining. Harrington scored five points during the spurt.
Dalembert kept the Sixers close with nine rebounds in the third, giving him 16 total. But Philadelphia fell behind 73-69.
In the first half, Green scored 15 points on 7-for-15 shooting as the Sixers took a 55-44 lead into the locker room.
Notes
The Sixers played without G Lou Williams (back spasms) and F Marreese Speights (sprained right knee). Knicks C Eddy Curry missed the game with a sore right calf. … The Sixers outrebounded New York 54-38.