Williams tossed in a long jumper to beat the halftime buzzer, then had 14 points in the final 3:28 of the third quarter, when the 76ers seized control for their third straight victory.
Andre Iguodala had 19 points, eight assists and seven rebounds for the 76ers, who turned a competitive game into a rout and end a three-game losing streak to the Knicks.
Carmelo Anthony scored 22 points but Jeremy Lin shot just 5 of 18 for 14 points for the Knicks. Tyson Chandler had eight points and 12 rebounds after missing two games with a strained left hamstring, but he couldn't solve the Knicks' defensive woes. Philadelphia was up by eight late in the third quarter before Williams took over. He made two 3-pointers, a pair of jumpers and four free throws as the 76ers outscored the Knicks 16-8 to open an 89-73 lead.
He nailed another 3 early in the fourth, and Turner followed with two free throws to push the lead to 21.
The Sixers have rebounded from a five-game skid before the All-Star break and followed a convincing victory over Boston by beating Utah.
The Knicks might have hoped to catch the Atlantic Division leaders at one point but now are simply hoping to hold onto a playoff spot after entering play just two games ahead of Milwaukee and Cleveland.
They dropped all four games on their road trip and looked particularly lost without Chandler, their defensive anchor. They yielded 118 points in a loss at San Antonio and surrendered 119 on Friday against Milwaukee.
But it's not only the defensive effort. Coach Mike D'Antoni concedes the intensity just isn't always there from his team, saying the Knicks sometimes get "lost" or "sidetracked."
And the crowd is recognizing it.
The building was often quiet, fans perhaps a little groggy after the clocks sprung forward and with an early start. But the Knicks also are not entertaining them the way they did during their seven-game winning streak last month. Lin has been solid but couldn't be expected to sustain his sensational level of play, and the Knicks are still unable to settle on their best rotation with a much deeper roster than they had back then.
Anthony, usually loudly cheered, had some boos sprinkled in when he was introduced with the starting lineups. A brief "Fire D'Antoni!" chant broke out in the final minutes, and there were some loud boos near the finish.
The Knicks led 24-22 after one quarter behind 12 points from Anthony. But New York turned it over six times in the second, and the 76ers went up 51-49 after Williams hit a long jumper from the corner as the first half ended.
Notes: The Sixers are 25-17 after they were 17-25 through 42 games last season. .. Sixers coach Doug Collins said center Spencer Hawes, who has a strained left Achilles and has missed 28 games, could play 2-on-2 Monday and increase his workouts throughout the week. ... D'Antoni didn't rule out forward Jared Jeffries (sore right knee) for Monday at Chicago but is aiming more for Wednesday or Friday.
