Kristaps Porzingis and the Knicks were riding high at the start of their Sunday matinee, but the fourth quarter was forgettable and regrettable for both.

Porzingis was posterized by Rudy Gobert’s emphatic left-handed slam and then had his dunk attempt stopped by the big Frenchman late in the game.

The Knicks didn’t stop much on the defensive end in the fourth quarter. They squandered a 13-point first-half lead, gave up 36 points in the final period and fell to the Jazz, 114-109, before a disappointed crowd at Madison Square Garden.

“Our defense with this team is going to spark everything,” an upset Derrick Rose said. “Our defense is everything with this team, nothing else.”

Rose seemed exasperated because it’s been a familiar theme for the 2-4 Knicks, who looked little like the team that won impressively in Chicago Friday night. Their offense was too much one-on-one and their subpar pick-and-roll defense led to too many one-on-nones for the Jazz.

“It hurts losing,” Rose said. “I ain’t going to sit here and lie to you. It hurts . . . But we got to learn from it.’’

With the Knicks continuing to have defensive breakdowns, Utah shot 13-for-20 in the fourth quarter. Yet the Knicks still had a shot late if they could make a defensive stand.

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Ahead 106-101 in the final minute, the Jazz had a side out-of-bounds play. The Knicks put two on the ball, but no one rotated back and George Hill found a wide-open Rodney Hood for a dunk with 35.3 seconds left, leading to groans from the fans.

Players pointed to a lack of communication on that play, but it was constant throughout the fourth quarter.

“We had a couple of breakdowns,” Jeff Hornacek said. “They were running a 1-3 pick-and-roll and we had some breakdowns on that. One guy thought they were switching, the other guy didn’t. Guys said they were yelling it out, other guys were saying they didn’t hear it.”

Porzingis scored 14 of the Knicks’ first 20 points and finished with 28, matching Carmelo Anthony’s output. Rose had 18 points and eight assists.

Jazz forward Gordon Hayward had 28 points, going 14-for-14 from the free-throw line, in his season debut. He missed the first five games with a fractured finger on his left hand. Hill had 23 points and nine assists.

“This is a game that I felt we kind of let slide or slip away from us,” Anthony said. “We gave this game away.”

The Knicks were in a giving mood.

Clinging to an 80-78 lead to start the fourth quarter, Hornacek opened the quarter with no starters on the floor. The lineup of Brandon Jennings, Justin Holiday, Mindaugas Kuzminskas, Lance Thomas and Kyle O’Quinn yielded seven consecutive points.

“You can’t play your starters the whole game,” Hornacek said.

After a timeout, Hornacek brought back starters Rose, Porzingis and Courtney Lee. But a miss and a Utah basket gave Utah an 87-80 lead.

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The Knicks moved within 90-87 on Lee’s three-pointer with 7:42 left, but the Jazz made it 96-87 after back-to-back baskets by Hood, the second a three-pointer.

Rose attacked and had two three-point plays in the next two minutes, helping the Knicks get within 100-95. But Hayward drilled an open jumper, and after a turnover by Lee, Hayward’s dunk gave Utah a 104-95 lead with 3:09 remaining. After Anthony scored, the 7-1 Gobert dunked over Porzingis to make it 106-97. Two possessions later, Gobert denied Porzingis’ dunk.

“Now I know how guys feel with me,” Porzingis said. “Those long arms, and his shot-blocking ability . . . Those type of players can change the game and make the defense really worry about you.”

It’s time for the Knicks to start worrying about their defense.