MEMPHIS, Tenn. — It was valiant. It was gutsy. It wasn’t good enough.

Certainly not the first half and definitely not the overtime execution.

The Knicks overcame a 19-point deficit, and they had opportunities late in regulation and the extra session to overcome Ja Morant and the Grizzlies. When the game was there for the taking, the big play eluded them at both ends of the floor.

“In the NBA, you can’t start off like that,” said Isaiah Hartenstein, one of the better Knicks in his debut in the orange and blue, referring to the poor first half that saw the Knicks outscored by 15.

Julius Randle fouling out early in the extra session proved crucial, as did RJ Barrett’s ugly 3-for-18 John Starks shooting impersonation. Jalen Brunson missed all four of his shots in overtime after his two clutch plays in the final seconds of regulation forced another five minutes. The result was a frustrating, 115-112 overtime loss to the shorthanded Grizzlies at FedExForum on Wednesday night.

Tyus Jones’ tie-breaking 3-pointer with 47.7 seconds provided the deciding margin, as the Knicks missed their final four shots — including Evan Fournier’s 3-pointer at the buzzer that would’ve extended the game to a second overtime. It capped a frustrating evening that saw the Knicks start poorly, play inspired, but come up short when it mattered most.

“What I want them to see is it’s one or two plays here or there, that’s the difference between winning and losing,” coach Tom Thibodeau said.

After a slow start, Brunson performed well — finishing with 15 points, nine assists and six rebounds. Hartenstein added 16 points, eight rebounds and four assists in 40 minutes off the bench subbing for the foul-plagued Mitchell Robinson, and Randle notched 24 points, 11 rebounds and six assists. Perhaps the biggest surprise was Reddish’s 22-point showing in a reserve role. Morant led all scorers with 34 points and nine assists.

“He’s an elite player in the league,” Hartenstein said.

Brunson’s layup with 3:32 left in regulation gave the Knicks their first lead since the early going, only for Memphis to respond by converting on five straight possessions. The Grizzlies went up four on Morant’s three-point play following a Steven Adams tip back. The Knicks got within one on Hartenstein’s three-point play with 28.9 seconds left, but Morant answered with a left-handed drive. Brunson then set up a game-tying Cam Reddish left-corner 3-pointer and drew a charge in the lane on Morant with 0.5 seconds to go, forcing overtime.

“That was a great play,” Thibodeau said. “That’s who he is. Giving his body up for the team. To me, that’s the definition of a playmaker.”

The Knicks got themselves back into the game on the strength of a determined third quarter. The offense functioned its best in the stanza, and the defense slowed down the Grizzlies. After Robinson picked up his fourth foul early in the quarter and the Knicks down 18, the ball-moving, rim-protecting, court-spacing Hartenstein spurred a comeback as they outscored Memphis by 12 over the final 10 minutes of the period. Randle’s left-wing 3-pointer made it a three-point game, and the large crowd was in stunned silence.

“We just kept fighting. We kept chipping away, chipping away,” Brunson said. “We can’t lay down when we’re getting beat like that. How are you going to respond? We responded well. It’s a sign of a team that wants to fight. So just start the game hungry, start the game that way and kind of have that mindset the full 48.”

The Knicks will have fewer than 48 hours to agonize over the loss, as they host the rebuilding Pistons at the Garden for their home opener Friday night. There was a lot to like from this one, even if it wasn’t the desired result. The newcomers played well. The ball moved on offense. The defense responded after some shaky stretches.

“I feel like if we play with that type of energy, effort and we just clean up a few details,” Randle said, “we’ll win a lot of games.”