Raymond Felton had his first career triple-double with 23 points, 11 assists and 10 rebounds as the Suns matched their worst home loss since 2000. Phoenix lost by 25 at home to Memphis late last season.
Stoudemire, given a rousing ovation when he was introduced, had 19 by halftime. But it was the Knicks' sharpshooters, looking much like the high-flying Suns of old, who turned the game into a blowout with a 3-point barrage in a 38-point third quarter.
New York's 17 3s, in 33 attempts, matched its season high and tied for second-most in franchise history.
Six Knicks sank 3s in their most one-sided win of the season, led by Felton's 5 of 10. Wilson Chandler scored 16, Shawne Williams 15 - going 4 of 9 on 3-pointers - and Landry Fields 14 for New York in its first stop on a four-game trip through the West.
Vince Carter scored 19 and Goran Dragic 17 for the sinking Suns, who have lost seven of eight and 11 of their last 14.
Seldom-used Knicks center Timofey Mozgov was ejected from the game for elbowing Robin Lopez with 3 1/2 minutes to play.
New York led 55-45 at the half, then turned the game into a blowout with a 14-0 third-quarter outburst. Williams had a three-point play and two 3s in the run, Felton hit a 3, then capped the run with a lob to Stoudemire for an emphatic dunk, the power forward pumping his fist in triumph before his feet hit the ground.
Stoudemire played eight seasons with the Suns, making five All-Star teams, before signing a five-year, $100 million contract with the Knicks. He is off to the best start of his career, entering the game as the league's No. 2 scorer behind Kevin Durant.
The game was a glaring example of the Knicks' rise in confidence and the Suns' fade with a mishmash of wing players and no strength in the middle.
New York took its biggest lead with a 14-5 run, punctuated by Williams' 3-pointer, that made it 115-81 with 5:16 to play and most of the crowd long gone.
Notes: The Knicks play the Lakers in Los Angeles on Sunday night. New York has lost six straight to the Lakers with its last win coming Feb. 13, 2007, in Los Angeles. ... Lopez, a former starter in coach Alvin Gentry's doghouse, didn't get into the game until there was just over six minutes to play. ... The Suns and Knicks meet in New York on Jan. 17. ... Phoenix had won six of the last eight against the Knicks. ... The Knicks earned their 21st win, something they didn't do last season until March 3.