Kyrie Irving has been fined $50,000 by the NBA after appearing to raise his middle finger to fans on two separate occasions during Game 1 of the Brooklyn Nets' playoffs opener against the Boston Celtics.

Irving defended his actions during the Nets' 115-114 loss to the Celtics on Sunday.

The 30-year-old, who played for Boston for two turbulent seasons before a sour exit in 2019, has been regularly booed by fans at the TD Garden, and the ill-feeling has only intensified with each meeting.

Irving scored a game-high 39 points in Sunday's loss, and insisted he was only reciprocating the feedback from the Celtics fans.

"Look, where I'm from, I'm used to all these antics and people being close nearby," Irving said post-game. "It's the same energy, and I'm going to have the same energy for them.

"And it's not every fan. I don't want to attack every fan, every Boston fan, but when people start yelling 'p****' or 'b****' or 'f*** you' and all this stuff, there's only but so much you take as a competitor.

"We're the ones expected to be docile and humble, take a humble approach. F*** that, it's the playoffs. It is what it is."

On Tuesday it was confirmed by the NBA that Irving would be fined for his actions, with a statement released by NBA Communications saying: "Brooklyn Nets guard Kyrie Irving has been fined $50,000 for making obscene gestures on the playing court and directing profane language toward the spectator stands, it was announced today by Byron Spruell, President, League Operations.

"Irving made the gestures and his comments to the spectators during the Nets' 115-114 loss to the Boston Celtics on April 17 at TD Garden."

Game 2 will take place at TD Garden on Wednesday.