James, 41 and entering a record-extending 24th NBA season with his fourth team, scored 14 points and handed out seven of the 76ers' 28 assists in a tantalizing glimpse of how he will be a facilitator for younger teammates like Tyrese Maxey - who led all scorers with 28 points.
"I could be a lot better," James told broadcaster NBC. "Still getting my rhythm, obviously just a little bit over two weeks with the new squad.
"But I like the way we played. I think we played exceptionally well, especially defensively."
Jaylen Brown, the former Boston Celtics star who arrived in Philly in a stunning trade for Paul George in July, scored 19 points with eight rebounds and six assists and center Joel Embiid added 13 points and 11 rebounds for the 76ers.
Jalen Brunson led the Knicks with 21 points and Karl-Anthony Towns scored 19 points with 12 rebounds, but after regaining the lead in the third quarter the 76ers repelled every Knicks charge.
The Knicks ended a 53-year title drought with their victory over the San Antonio Spurs in last season's NBA Finals.
Knicks legends including Bill Bradley, Earl Monroe and Walt Frazier handed out the Knicks' championship rings in an emotional pre-game ceremony at the Garden, where the crowd featured die-hard celebrity Knicks fans like Ben Stiller and Spike Lee along with other famous faces including rocker Jon Bon Jovi and NFL commissioner Roger Goodell.
Before the club's third championship banner was raised to the rafters, NBA Finals Most Valuable Player Brunson told fans the Knicks were "ready to turn the page as a team.
"But one thing I would like to say - the joy that this city had this summer we'd love to replicate that again," Brunson said of a Knicks team aiming to be the first repeat champions since 2018.
James, a four-time NBA champion and the league's all-time leading scorer, admitted that winning on another team's ring ceremony night was especially satisfying.
"It's pretty special," he said.
Both teams were slow to fire offensively. James scored his first points for his new team with a layup that cut the deficit to 19-18 late in the first quarter.
The Knicks pushed their lead to 10 three times in the second quarter, but the Sixers chipped away and trailed by four at halftime.
A 76ers steal culminated in Brown's alley-oop pass to James for a basket that pulled the Sixers within one early in the third quarter and James's running layup put Philadelphia back in front, 64-63.
They would trade the lead before the 76ers pulled away for good, hanging on after New York cut the deficit to one late in the final period.
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