The Knicks didn’t lose to “Playoff Jimmy.”

Their undoing was their own.

Their inability to throw the ball in the ocean from 3-point land on top of the absence of leading scorer Julius Randle started this Eastern Conference semifinal on a sour note.

Up 12 and seemingly in control most of the first half, the Knicks were thoroughly outplayed over the final 24 minutes in a dismal 108-101 Game 1 loss to the Heat at a disappointed and sold-out Garden.

The Knicks shot just 7-of-34 from 3-point range after entering this series as the worst 3-point shooting team in the playoffs, making only 28.2 percent.

They were within striking distance, down just three with 5:05 left when Jimmy Butler appeared to hurt his right ankle.

But they managed just two points over the next 4:02, blowing any chance to come from behind.

Butler was typically brilliant, scoring 25 points along with 11 rebounds and four assists, and he had plenty of help.

Kyle Lowry scored 18 points off the bench and Bam Adebayo added 16 points and seven rebounds, while controlling Mitchell Robinson in the paint.

RJ Barrett had 26 points, nine rebounds and seven assists for the Knicks and Jalen Brunson had 25, but both struggled in big moments in the fourth quarter.

The Knicks mostly controlled the game over the first 24 minutes – everywhere but the 3-point line, where they were outscored by 12.

They entered the game last in the postseason in 3-point shooting, and were 3 of 16 from distance in the opening half.

It kept the Heat in the game, as they were otherwise outplayed in every other facet.