It was everything the Garden envisioned — but in green and white.

Ten years after being picked as the Knicks’ future, Kristaps Porzingis delivered one of his top career displays to hand his old team a devastating defeat. He put up an impressive 34 points (making 8 out of 13 3-pointers), which notably included the game-winning basket in overtime with just 41.2 seconds remaining, leading the Celtics to a 119-117 victory on Tuesday night at Madison Square Garden.

“Playing here, it’s always really fun,” Porzingis said. “The fans are super into the game. They love the Knicks. I enjoyed playing here as a home player and now also on the road.”

The former fan favorite started slow, scoring just two points in the first quarter, but soon unleashed a string of deep 3s, taking advantage of the wide-open looks repeatedly offered.

The injury-prone big man, who has been limited to 40 games this season, played the part of the “unicorn” that Kevin Durant discovered, the player with limitless potential and inimitable skill, whose lone All-Star Game selection came with the Knicks in 2018.

Leading the Celtics back from an early 11-point hole, Porzingis stole the show in the third quarter, hitting four 3-pointers, including a 39-foot bomb from the logo, which left the crowd in awe and angst.

“The ball rolled to me, I said, ‘This is destiny,’ ” Porzingis said. “I let it fly without thinking too much. Those are the best kinds of nights, just playing free and letting it fly and shots are going in. Once I saw the ball kept going in, I let it fly without thinking. It was a good night.”

Porzingis took a back seat in the fourth quarter as Jayson Tatum took over.

Then, the 7-foot-2 Latvian hit a pair of free throws to break a tie with 1:51 remaining in overtime.

After Jalen Brunson’s jumper evened the game at 112, Porzingis made one of his biggest shots in the building.

As Karl-Anthony Towns helped on a driving Derrick White, Porzingis stepped back deep beyond the arc, receiving the kick out and easily hitting the 3 over the outstretched arms of Brunson.

“They did a late switch and I created a little separation,” Porzingis said. “It was a pretty deep one and I just let it fly without conscience. We were just making plays for each other down the stretch … I’m happy with the way we responded and came out with the win.”