Anthony, who was angry about Garnett's choice of words during a fourth-quarter altercation, went toward the Celtics' locker room after the game and later waited for Garnett outside Boston's team bus.
Anthony didn't believe he would be suspended because he said he was just looking to talk to Garnett, not fight. But NBA executive vice-president of operations Stu Jackson ruled otherwise.
"There are no circumstances in which it is acceptable for a player to confront an opponent after a game," Jackson said in a statement. "Carmelo Anthony attempted to engage with Kevin Garnett multiple times after Monday's game and therefore a suspension was warranted."
Anthony will miss the Knicks' nationally televised game at Indiana on Thursday and lose about $176,700 of his $19.4 million salary.
Jackson said Anthony confronted Garnett "in the arena tunnel, near the players' locker rooms, and in the parking garage." The incident by the bus, with New York police and Knicks coach Mike Woodson nearby, was captured on videotape.
Anthony and Garnett received technical fouls with 9:03 remaining in the Celtics' 102-96 victory, arguing with each other from the baseline to midcourt after a physical exchange on Boston's previous possession. After the game, Anthony went the wrong direction toward the Celtics' locker room in hopes of finding Garnett.
On Tuesday, Anthony said he was upset because of what Garnett said, though wouldn't elaborate on what it was.
"There's certain things that you just don't say to men, another man," said Anthony, who is married to actress LaLa Vasquez.
"It's over with for me. Whatever happened last night, happened. The words that was being said between me and Garnett, it happened, can't take that away," Anthony added. "I lost my cool yesterday, I accept that, but there's just certain things that push certain people's buttons."
Anthony was clearly affected by Garnett, shooting just 6 of 26 from the field after averaging 36 points last week while winning Eastern Conference player of the week honours. He said the All-Star forwards eventually spoke and sorted out the matter.
Anthony will be eligible to return Friday at home against Chicago. He was ejected from the last meeting with the Bulls after receiving two of his eight technical fouls this season.
Garnett was not penalized.