Knicks blow big lead in OT loss to Lakers

LOS ANGELES — The Knicks staged a storybook first half, collapsed in the second half, rose from the dead to force overtime and still lost in a rollercoaster contest to the Lakers on Saturday.

RJ Barrett forced overtime with a dramatic 3-pointer with 8.3 seconds left and finished with a career-high 36 points, but the Lakers squeaked out the victory, 122-115, at the newly named Crypto.com Arena.

The Knicks couldn’t steal the thunder from LeBron James’ triple-double return, even after overcoming their second-half nightmare.

The Knicks went stone cold in overtime — shooting just 2-for-11 — after Barrett brought them back from a nine-point deficit.

Barrett also defended James for a good part of the night — an assignment he requested.

“It’s a game we should’ve won,’’ Barrett said. “To come out the way we did, 71 points in the first half. Up by 20 in the first half. It’s a tough game to lose. I felt overall we obviously played well but not good enough.’’

James, after missing the last five games with knee issues, conveniently came back for the nationally televised contest against the team he loves to torture and rang up a triple-double — 29 points, 13 rebounds and 10 assists.

Still, Barrett said he wanted to take the James challenge.

“I was texting everybody trying to figure out [what assistant coach] had the scout so I could tell him I wanted to guard him,’’ Barrett said. “It was a tough matchup. He’s so smart. And physically he’s really strong. Sometimes it’s tough to stop him when he’s driving.’’

After pummeling the Lakers in the first half while building a 21-point lead, with Julius Randle and Barrett dominating, the Knicks fell to pieces in the third quarter, when they were outscored 31-13.

“The third quarter was problematic,’’ Tom Thibodeau said. “Then we had a good fight down the stretch. And didn’t get it done. There’s always good and bad in every game. My concern is we got to get it done.’’

But after falling behind by as many as eight points in the fourth quarter, the Knicks suddenly were alive again. Malik Monk missed a jumper and the Knicks raced down, with Evan Fournier feeding Barrett, who drilled a game-tying 3-pointer, making it 111-111 with 8.7 seconds left.

Despite the late heroics, they still fell a season-worst five games under .500 at 24-29 in kicking off a make-or-break western trip.

Randle finished with 32 points, 16 rebounds and seven assists. There were moments but just not enough.

“Just think if we play fast like we did, compete like we did, especially in the first half I feel like we can win and beat anybody,’’ Randle said. “We competed in the first half defensively, getting off. We haven’t been getting off to great starts all year, consistently, so we can build off of that. We just have to sustain it.’’

The disappointing Lakers (26-28) had all of their Big 3 healthy and Anthony Davis was a beastly presence in racking up 28 points and 16 rebounds. Monk crushed the Knicks for 29 points to make up for a dud game by Russell Westbrook (five points, 1-for-10 from the field).

This looked like it would become a statement win and instead disintegrated into a huge letdown for the Knicks because of all the promise they showed early in the contest five days before the trade deadline.

The second-half collapse was capped when Davis stole a rebound from Robinson and dunked it for a 80-79 lead — the Lakers’ first one — with 4:40 left in third. That capped a 25-7 start to the second half.

The Knicks trailed 87-84 entering the fourth quarter after being routed 31-13 in the third.

After Westbrook bricked two free throws with under a minute left in regulation, Alec Burks had a chance to bring the Knicks to within one point, but bricked a 3-pointer from the corner with 52.1 seconds left.

It was painful with Randle cooling off and then falling into a cameraman seated baseline. Randle came up clutching his shoulder before shooting free throws. He later got a technical foul for shouting from the bench with 28.9 seconds left in the third quarter.

Randle and Barrett played with ferocity in the explosive first half in scoring 20 and 21 points, respectively, but quieted down after intermission.

The Knicks notched a season-high for points in a first quarter with 41. They staked themselves to a 71-56 lead at halftime. They led 11-0 at the start and kept it up all half.

Barrett was brilliant in the first quarter by racking up 17 points, mixing it up with 3s and spinning, powerful drives.

“The way he’s played, he’s really the last five, six weeks he’s really…